Process and catalyst for dehydrogenation of organic compounds

ABSTRACT

The invention comprises a process for selectively oxidizing hydrogen in a mixture with other gaseous materials by contacting the hydrogen containing gas under oxidation conditions with a catalyst comprising a phosphate of a metal wherein the metal is selected from the group consisting of germanium, tin, lead, arsenic, antimony and bismuth.

This application is a divisional of application Ser. No. 08/399,617,fried Nov. 15, 1994, which is a continuation in part of application Ser.No. 07/874,499, filed Apr. 27, 1992, now U.S. Pat. No. 5,439,859.

BACKGROUND OF THE INVENTION

This invention relates to catalytic dehydrogenation of C₃ to C₁₀alkanes, especially normal or isobutane or methylbutanes or otherdehydrogenatable hydrocarbons, ethylbenzene for example.

Known processes for dehydrogenation of C₃ -C₁₀ alkanes to monoolefinsare capital intensive and demand high operating costs because of severeenergy requirements. Many of the existing processes for dehydrogenationof alkane fractions, particularly C₃ to C₅ fractions, to monoalkenes usecatalysts which rapidly deactivate and require frequent or continuousregeneration. This need often leads to additional process complexity orto large reactor volumes or low on-stream factors. The development ofselective and economical processes to provide mono-alkenes from alkaneswill facilitate the production of reformulated motor fuels, theutilization of low value high vapor pressure components in motor fuels,and the production of chemical products which are in high demand.

Conventional dehydrogenation processes have high operating and capitalcosts: The need for feed dilution and the unfavorable position of theequilibrium, resulting in relatively low conversion, necessitate largereactor vessels, which adds to capital costs. Furthermore, therequirement of frequent catalyst regeneration necessitates a furtherincrease in reactor volume (numbers of vessels in parallel or a separateadditional regenerator vessel) to enable concurrent or periodicregeneration of catalyst. Alternatively, as in the Oleflex orSnamprogetti-Yarsintez processes, a stream of catalyst can be circulatedbetween the main reactor and a regeneration vessel continuously. Thisrequires a complex physical arrangement and mechanical control systemand suffers from the requirement of additional catalyst inventory. Anexpensive precious metal based catalyst may be used, and catalystattrition during circulation may result in further catalyst expense orthe need for equipment to prevent environmental contamination fromcatalyst fines. An additional disadvantage of typical dehydrogenationprocesses is the high temperature of operation which is required tomaximize the product in these equilibrium limited systems. The highendothermicity of dehydrogenation requires a large heat input which inturn results in high capital costs for heaters, heat exchangers,reheaters etc, as well as in high operating costs for fuel. Oxidativedehydrogenation processes in which an oxygen source is a coreactantovercome the costs associated with low conversion and high heat inputrequirements, but known oxidative dehydrogenation processes aregenerally not sufficiently selective to monoalkenes, particularly whennormal alkanes are used as a feedstock. The present invention overcomesmany of the problems associated with the known art.

PRIOR ART

Processes in which catalytic dehydrogenation is followed by catalyticselective oxidation of hydrogen are disclosed in T. Imai et al, AICHENat. Mtg., New Orleans, March 1988, Preprint 64a, in T. Imai et al U.S.Pat. No. 4,788,371 and R. A. Herber et al U.S. Pat. No. 4,806,624.

Process in which hydrogen is cofed with alkane feedstock is disclosed inMiller U.S. Pat. No. 4,727,216 issued Feb. 23, 1988.

Processes in which alkanes are hydrogenolyzed using nickel andcopper-containing catalysts are disclosed in Carter et al, U.S. Pat. No.4,251,394, issued Feb. 17, 1981, J. H. Sinfelt et al, J. Catal. (1972),24, 283, J. A. Dalmon et al, J. Catal. (1980), 66, 214, Z. Popova et al,React. Kinet. Catal. Lett. (1989), 39, 27 and D. Nazimek, React. KinetCatal. Letter (1980), 13, 331. Other references disclosing usingnickel/copper catalysts for other reactions are B. Coughlan et al, J.Chem. Techm. Biotechnical (1981), 31, 593 and S. D. Robertson et al, J.Catal. (1975), 37, 424.

Catalysts consisting of chromia supported on alumina are disclosed foruse in dehydrogenation in U.S. Pat. No. 4,746,643 issued in 1988.Chromium treated silicas and silica-titanias are known as olefinpolymerization catalysts, P. McDaniel et al, J. Catal. (1983), 82, 98;110; 118. Additional prior art is described below.

EMBODIMENTS OF THE INVENTION

The invention provides ways of overcoming the disadvantages of the priorart dehydrogenation of alkanes and provides improvements in the resultsobtained in prior art processes. The invention has seven generalembodiments, each of which is further divided into sub-embodiments.

In the first embodiment, the invention relates to a multi-step processflow scheme which conserves heat by alternating endothermicdehydrogenation zones and at least one exothermic zone in which hydrogenis selectively oxidized; in this scheme, any known dehydrogenationcatalyst and any known catalyst for selective oxidation of hydrogen canbe used.

In the second embodiment of the invention, particular dehydrogenationcatalysts are used in dehydrogenation of dehydrogenatable compoundsgenerally whether or not according to the process flow scheme accordingto the above embodiment of the invention. These catalysts are sulfidedcatalysts containing nickel and an optional modifier such as compoundsor allotropes of tin, chromium , copper or others described infra on asupport of little or no acidity, for example supports such as asodium-exchanged or barium-exchanged zeolite, such as zeolite L ormordenite, or a cesium-treated alumina; sulfiding is particularlyeffective with preferred reagents described below in another embodimentof the invention; preferred catalysts also have particular porestructures, described infra and prepared according to yet anotherembodiment. An optional barrier layer, described below, may also beincorporated.

Nickel with optional addition of modifiers may also be supported on asupport consisting of a metal oxide such as alumina of a particular poresize distribution which has been precoated with a carbonaceous layercontaining little or no hydrogen. All of the nickel catalysts describedabove require activation prior to use, including a sulfiding step.

In a preferred mode of this embodiment, catalysts are activated bysulfidation in the presence of molecular hydrogen using particularreagents, consisting of compounds containing both carbon and sulfuratoms, preferably within certain ratios, and optionally containingoxygen atoms such as in dimethylsulfoxide. This treatment is followed bya coking procedure to provide an additional carbonaceous component tothe catalyst, preferably within certain ranges of weight percent carbon.This overall procedure results in catalysts which exhibit outstandingselectivity and activity in the dehydrogenation processes summarizedabove; inferior performance is observed if hydrogen sulfide is used as asulfiding agent exclusively.

The catalysts may be further improved by adjusting the acidity of asupport. For example, the acidity of alumina may be reduced by treatmentwith alkali components and, optionally, calcination to suppress coking,hydrogenolysis, and isomerization when the resulting support is used inthe preparation of a dehydrogenation catalyst which is used according tothe invention.

An optional procedure may also be applied to provide for an intermediatebarrier layer between the support oxide and the nickel component. Thislayer inhibits one type of deactivation by slowing the formation ofinactive compounds between nickel and the bulk support oxide. Forexample, a refractory metal aluminate layer may be preformed on analumina support by impregnating the support with a metal-containingmaterial, an organometallic compound for example, and calcining theimpregnated support at a temperature, 500° C. for example, at which ametal aluminate layer is formed on the support. Then the supportcontaining the metal aluminate layer is impregnated with an activemetal-containing material and calcined at a lower temperature, 200° C.for example. The preformed metal aluminate layer inhibits furtherreaction between alumina and nickel during catalytic processing stepsusing this catalyst.

In the third embodiment, useful catalysts are prepared by a combinationof leaching of solid metal oxide supports with liquid solutionscontaining carboxylic acids, for example oxalic acid, and calcination.This process adjusts support pore structure distributions to preferredranges which, among other benefits, increases the tolerance of thecatalyst to coke deposition and enables relatively severe reactionconditions to be used without undue deactivation of the catalyst. Thepreferred pore size ranges are described infra.

A temporary pore blocking reagent can then be impregnated selectivelyinto the remaining small pores to block access to small pores duringimpregnation with a liquid solution containing a nickel compound in asolvent which is immiscible or poorly miscible with the temporary porefilling reagent. This technique results in a skewed nickel depositionafter drying and subsequent treatment such that a higher nickelconcentration is deposited within larger pores than within pores ofsmaller radii. These supported nickel materials are then sulfided andfurther activated, as described in detail later, and become catalysts oflong useful lives on-stream and of high selectivity as illustrated inexamples. This pore blocking technique is applicable to porous supportsgenerally, for temporary blocking of the smaller pores in the support.

In the fourth embodiment, an effective dehydrogenation catalyst consistsof sulfided nickel supported on a carbon coated metal oxide supportwhich also features a particular pore size distribution. Compositions ofthis type are superior to typical bulk carbon supported nickel catalystwhich do not contain a pore modified metal oxide, in their effectiveuseful on-stream lives when used in dehydrogenation processes accordingto this invention.

In the fifth embodiment, a Group IVB or VB metal phosphate such as tinphosphate is used to catalyze the selective oxidation of hydrogen in amixture thereof with hydrocarbons and a source of oxygen. The Group IVBor VB metal phosphate catalyst can be incorporated on the surface of orwithin the pore structure of an otherwise inert porous monolithicceramic body with efficient heat transfer properties. Other supportstructures such as the bonded porous metal bed described in Europeanpatent application EP416,710 and incorporated herein by reference, mayalso be used. Alternatively neat formed particles of the dried gelledcatalysts may be used; preformed porous inert supports may beimpregnated by the catalyst precursors, then calcined to form activecatalysts.

In the sixth embodiment, the sulfided, non-acidic, nickel-containingdehydrogenation catalysts of this invention as described above andoptionally prepared by the methods described above, are used in aparticular multi-step process for dehydrogenation of dehydrogenablehydrocarbons, particularly C₃ -C₅ alkanes, in which endothermicdehydration zones containing the nickel catalyst alternate betweenhydrogen combustion zones which contain hydrogen combustion catalyst andto which a source of oxygen is fed. Hydrogen may be cofed along withhydrocarbon feed, preferably within the range of 0.2 to 1.2 moles ofhydrogen per mole of hydrocarbon feed; and most preferably within therange of 0.3 to 0.6 mole of hydrogen per mole of hydrocarbon.

In the seventh embodiment, the multi-step process described above inwhich dehydrogenation reactor zones alternate with hydrogen combustionzones is performed using particular dehydrogenation catalysts of thisinvention consisting of sulfided nickel on non-acidic supports and/orparticular hydrogen combustion catalysts of this invention, supra. Thisembodiment, which requires the use of particular catalysts both fordehydrogenation and also for hydrogen combustion as well as a particularprocess flow scheme and reactor type, results in economic advantageswhen compared to other known dehydrogenation processes.

Each of the embodiments summarized above is described below in greaterdetail and with the help of examples.

DESCRIPTION OF THE DRAWINGS

The invention will be further described with reference to the attacheddrawings, in which

FIG. 1 illustrates a dehydrogenation process in which dehydrogenationzones alternate with zones in which hydrogen is selectively oxidized togenerate heat for the next dehydrogenation zone,

FIG. 2 shows the differential ratio of pore volume to pore radii,DVP/DRP, for fresh and for spent Ni-Cu/Ba L zeolite catalyst as afunction of pore radius;

FIG. 3 is a similar chart for Ni-Cs/alumina catalyst having the poreradius distribution according to one embodiment of the invention.

FIG. 4 shows percent pore volume loss caused by coke deposits as afunction of carbon content for Ni-Cr/L zeolite catalyst and forNi-Cs/alumina catalyst having the pore radius distribution according toone embodiment of the invention;

FIG. 5 shows the yield of dehydrogenated product as a function ofreaction time for Ni-Cr/L zeolite at hydrogen to hydrocarbon mole ratioof 2.0 in a particular reactor system, and for Ni-Cs/alumina catalysthaving pore radius distribution according to one embodiment of theinvention, at hydrogen to hydrocarbon ratio of 0.5;

FIG. 6 shows DVP/DRP as a function of pore radius for fresh alumina andfor alumina calcined at 1080° C.;

FIG. 7 shows DVP/DRP as a function of pore radius for fresh AlcoaCSS-105 alumina and for CSS-105 alumina which has been leached with hotaqueous oxalic acid and calcined;

FIG. 8 shows the ammonia temperature programmed desorption peak areas asa function of temperatures for the following catalysts: (a) 8% Ni and 3%Cs on Al₂ O₃, (b) 8% Ni and 7% Cs on Al₂ O₃ and (c) 3% Ni and 3% Cs onpre-calcined Al₂ O₃ ;

FIG. 9 shows a comparison of isobutane dehydrogenation rates for asulfided nickel-cesium catalyst and two platinum-based catalysts;

FIG. 10 shows the effect of a barrier layer on the catalystreducibility;

FIG. 11 is an electron microscopic image of a catalyst containing 8% Niand 7% Cs on alumina and containing, after use as a dehydrogenationcatalyst 34.9% carbon;

FIG. 12 shows yield of dehydrogenated product as a function of time fora catalyst containing 8.3% and 7% Cs on alumina, during its use indehydrogenation of isobutane at 600° C. after sulfiding withdimethylsulfoxide at a hydrogen/isobutane ratio of 1.0;

FIG. 13 shows the ratio of initial reaction rate to deactivation rate asa function of hydrogen/isobutane ratio, and

FIG. 14 shows a reactor which may be used in selective oxidation ofhydrogen.

MULTI-STEP PROCESS

The invention is, in the first embodiment as listed supra, a multi-stepprocess for dehydrogenation of alkanes in which alkane plus hydrogenmixtures are passed through alternating endothermic catalyticdehydrogenation zones and at least one exothermic catalytic oxidationzone. These zones may be incorporated within a single reaction vessel soas to provide an adiabatic or near adiabatic reaction environment.

In the multi-step process embodiment of the invention, alkane-containingfeed is contacted with dehydrogenation catalyst in each of a pluralityof dehydrogenation zones to produce hydrogen and dehydrogenatedhydrocarbon product. The hydrogen and dehydrogenated products producedare then contacted with oxidation catalyst and an oxygen-containing gasin each of said oxidation zones to selectively oxidize a portion of thestream and generate heat. The effluent from each oxidation zone alongwith heat produced are then routed through another dehydrogenation zoneto produce additional hydrogen and dehydrogenated product. Hydrogen isseparated from the reactor effluent in a separate process step usingtechniques known in the art, and a portion of the separated hydrogen isrecycled with fresh feed and/or unreacted hydrocarbon feed to adehydrogenation zone, preferably the first such zone in the adiabaticreactor train. Infrequent periodic regeneration of the dehydrogenationcatalyst may be performed by passing an oxygen containing gas throughthe dehydrogenation catalyst zones as well as the oxidation catalystzones for a time sufficient to remove excessive coke deposits, but notall coke deposits, followed by passing hydrogen and certain sulfurcompounds through this zone to reactivate the catalyst.

In one embodiment of the multi-step process of the invention, there aretwo dehydrogenation zones and one catalytic oxidation zone. The productsfrom the first dehydrogenation zone, which are reduced in temperaturebecause of the endothermic nature of the dehydrogenation process, arecontacted with oxidation catalyst in the oxidation zone to selectivelyoxidize a portion of the hydrogen in the product mixture, leavinghydrocarbons in the product mixture mainly unoxidized to oxygenated orcombustion products. The selective oxidation generates heat whichprepares the mixture for dehydrogenation of undehydrogenated alkanesremaining in the mixture, in the second dehydrogenation zone. Some heatmay also be transferred to the preceding dehydrogenation zone; water andhydrogen are removed from the product mixture from the seconddehydrogenation zone; and a portion of the removed hydrogen is recycledto the first dehydrogenation zone.

In other embodiments of the multi-step process of the invention,additional alternating dehydrogenation and oxidation zones are provided.For example, three dehydrogenation zones alternate with two oxidationzones. The products from the second dehydrogenation zone containundehydrogenated alkanes, and the product mixture is reheated in thesecond oxidation zone by selective oxidation of hydrogen therein, andthe reheated product is further contacted with dehydrogenation catalystin the third dehydrogenation zone. Water and hydrogen are separated fromthe products from the third dehydrogenation zone, and a portion of thehydrogen is recycled to the first dehydrogenation zone. This is theoperation shown in FIG. 1 described below. More than threedehydrogenation zones and more than two selective oxidation zones arewithin the scope of this embodiment of the invention, but are notpreferred.

The catalyst employed in the dehydrogenation zones in the multi-stepprocess according to this embodiment of the invention may be any knowncatalyst for dehydrogenation of alkanes, such as for example thecatalysts disclosed in Miller U.S. Pat. No. 4,726,216 (Feb. 23, 1988).Alternatively, the catalyst may be one of the dehydrogenation catalystsdescribed infra whose use in dehydrogenation processes generally is partof this invention. Alternatively, the catalyst may be one of the novelcatalysts described infra.

In one embodiment, the catalyst employed in the oxidation zones of themulti-step process of this embodiment of the invention, for selectiveoxidation of the hydrogen component without burning much of themonoolefin or alkane in mixtures of hydrogen and hydrocarbons, may beany known catalyst for such selective oxidation, such as for example thecatalysts disclosed as useful in the StyroPlus process as disclosed inT. Imai et al supra or in the Miller patent supra or the Pt/Sn/Cs/Al₂ O₃catalyst described in T. Imai et al U.S. Pat. No. 4,788,371 (Nov. 29,1988).

In another embodiment, the catalyst employed in the oxidation zones forselective combustion of hydrogen can be the novel catalysts describedinfra whose use is part of this invention.

In one embodiment of the invention, a cofeed of hydrogen and optionallyppm levels of H₂ S are passed along with the alkane over the noveldehydrogenation catalyst of this invention; at particular hydrogen toalkane ratios, as subsequently disclosed, the ratio of initialdehydrogenation rate to average catalyst deactivation rate is maximized.Operations using preferred ratios of hydrogen to alkane, with the novelcatalysts of this invention infra, result in optimal alkene yield overthe on-stream life of the catalyst between regenerations, and obviatethe need for frequent regeneration to remove coke on catalyst.Hydrogenolysis over the novel catalysts of this invention, infra, issuppressed by at least initial sulfiding with particular reagents and byappropriate catalyst design. A single initial sulfidation of the novelcatalysts after each oxidation cycle in our process using preferredreagent is usually favored, but under some circumstances continuoussulfidation with sources of sulfur such as hydrogen sulfide or othersulfur-containing compounds is acceptable after initial sulfidation witha particular type of sulfur compound. Sulfur-containing impurities inthe feedstock may serve the purpose of providing continuous sulfidation.

In the multi-step process according to one embodiment of the invention,reactants, product olefins, feed hydrogen, and additionally producedhydrogen leave the dehydrogenation zone of a compound adiabaticpacked-bed reactor and pass into a zone in which a portion of thehydrogen is selectively burned. Internal heat is provided in the rightamount to balance the heat requirement for dehydrogenation and make theprocess thermoneutral. Typically, the hydrogen oxidation is controlledby the air or oxygen inlet rate such that about half or less of thehydrogen produced by dehydrogenation is consumed, since the heat ofexothermic hydrogen oxidation is about twice that of the endothermicdehydrogenation. The heat produced via the exoergic hydrogenolysisreaction to yield principally methane by-products satisfies a portion ofthe heat input required for dehydrogenation and serves to reduce theamount of hydrogen required to be combusted in the oxidation zone. Hencethe process is a net producer of hydrogen. Successive stages of hydrogenoxidation followed by dehydrogenation are stacked within the reactor.The hydrogen combustion zones should be sufficiently large to enablecomplete consumption of oxygen since breakthrough of oxygen into thedehydrogenation zone is detrimental. Porous ceramic hydrogen combustionzones may be used. The hydrogen combustion catalyst is contained withinthe pore structure of the catalyst support or on the surface of aceramic monolith or is used neat. Oxygen may be fed orthogonally throughthe ceramic structural pores so that bulk mixing of either product orfeed hydrocarbons or of hydrogen does not occur with oxygen prior tocontact with active catalyst surface. Using the novel catalysts of thisinvention, the volume ratio of the combustion zone catalyst todehydrogenation zone catalyst will preferably be 0.1 to 0.25 if packedbeds of similar packed bed density are utilized in both zones.

According to the multi-step embodiment of the invention, at least twodehydrogenation zones and at least one selective oxidation zone may beemployed in alternating fashion; larger numbers of such zones may alsobe used. A number of zones of unequal size may be interspersed in thereactor to maintain even heat distribution despite diminished heatabsorption with each successive dehydrogenation stage as dehydrogenationequilibrium is approached. The worsened position of equilibrium due tomass action toward the reactants caused by hydrogen addition may becompensated for in part by the shifted position of equilibrium towardthe product olefins as hydrogen is burned.

Control of the temperature in the dehydrogenation zones may beaccomplished by adjustment of the feed rate and/or the oxygenconcentration of the oxygen-containing gas to the hydrogen combustionzones. A diluent gas, for example, steam, may be fed along within theoxygen-containing gas into the combustion zones. Preferred temperatureof operating the dehydrogenation zones varies depending on thefeedstock, but is typically between 500° C. and 630° C.

Any means of separation of hydrogen from hydrocarbons and water can beused in the process such as the hydrogen recycle loop shown in FIG. 1.For example, membrane separation, pressure swing absorption techniques,or turboexpander techniques can be used. Capital cost requirementsdictate the method of choice. Other aspects of the process hardware ofthe invention such as pumps, compressors, heaters, etc. are thosegenerally useful and suitable.

Other processes are known which pass oxygen into a dehydrogenationreactor to selectively burn hydrogen. These include the "StyroPlus"process for ethylbenzene dehydrogenation (see Imai et al AIChE Nat.Mtg., New Orleans, 3/88 Preprint 64a 20p supra; Process Engineering(London),(1988), 69, 17), and the process disclosed in R. A. Herber etal, U.S. Pat. No. 4,806,624 (Feb. 21, 1989). The present process differsin one embodiment from these known processes by virtue of circulatingadditional hydrogen beyond that which is produced by catalyticdehydrogenation and of not requiring substantial quantities ofadditional steam cofeed along with hydrocarbon feed. Steam generation isexpensive and forces the use of larger reactor vessels due to the highsteam to hydrocarbon ratios required in the Herber et al patent. Theadditional hydrogen and the particular hydrogen to hydrocarbon ratio ofour preferred embodiments result in greater time on stream betweenregenerations, enabling economical operation, a factor not recognized inthe Herber et al patent.

Dehydrogenation in the presence of hydrogen cofeed is disclosed in theMiller patent supra. The disclosed procedure of this patent does nothowever require nor recognize the advantage of selective hydrogencombustion. Another distinguishing feature of one embodiment of thisinvention is the use of catalysts as subsequently described, for optimumperformance. The subsequently described catalysts may be more selectiveand have greater onstream life than the catalyst of the Miller patentwhen dehydrogenating in the presence of hydrogen cofeed, particularly atthe preferred hydrogen to alkane feed ratios of the invention. Also, thecatalysts of the invention, using nickel plus other lesser quantity ofmodifier, rather than platinum as in the Miller patent are expected tohave lower material costs. The process of the invention uses a sulfidedcatalyst, but as disclosed below, uses in one embodiment a sulfidingagent not suggested in the Miller patent supra, thereby obtaining longeronstream life and shorter induction periods during which the catalyst isactivated.

Imai et al U.S. Pat. No. 4,788,371 supra discloses alternatingdehydrogenating and hydrogen oxidation zones (column 10, lines 22-28)but uses the same catalyst in all zones, whereas applicants' processadvantageously uses different catalysts in the dehydrogenation andhydrogen oxidation zones. Imai's dehydrogenation process is typicallyconducted in the presence of a large amount of steam, the ratio of steamto hydrocarbon being 2.07 moles of steam to 0.7 mole of hydrocarbon inTable 1 for example; whereas, applicants' process preferably uses noadded steam, or no more than 0.5 mole of steam per mole of hydrocarbon.Added steam, if used in applicant's process is a minor amount of thereaction mixture. Use of hydrogen as in applicants' process is moreeffective against coking of the catalyst than the use of steam.

The Herber et al patent supra discloses catalytic dehydrogenation ofhydrocarbons, followed by catalytic selective oxidation of hydrogen inthe dehydrogenation product and indirectly heat exchanging the oxidationproduct with fresh feed to the dehydrogenation to preheat the latter;the oxidation zone effluent stream is not contacted with dehydrogenationcatalyst. In applicant's process, the oxidation product is passed into asecond dehydrogenation zone to dehydrogenate feed hydrocarbon which wasnot dehydrogenated in the first dehydrogenation zone. In one embodimentof applicant's invention, for better control of the overall reaction,the temperature differential in each of the dehydrogenation zones isless than 25° C. between the inlet and outlet of the zone, and asufficient number of dehydrogenation zones is used to obtain the desiredoverall conversion.

Imai et al, The Principle of Styro Plus, AIChE Nat. Mtg. New Orleans,3/88, Reprint 64a, supra, discloses alternating steam dehydrogenationand hydrogen oxidation zones (page 6). The dehydrogenation catalyst isapparently a potassium promoted iron catalyst (page 5). The selectiveoxidation catalyst is a proprietary catalyst, apparently different fromthe dehydrogenation catalyst. The feed to the first dehydrogenation zoneapparently consists of steam and hydrocarbon. The hydrogen produced in adehydrogenation stage is more than enough to provide, by selectiveoxidation thereof, the heat needed for the next dehydrogenation stage.Apparently, no additional hydrogen is supplied to the process.Applicants' process uses only minor amounts of steam at most, andsupplies additional hydrogen to the dehydrogenation process.

CATALYTIC DEHYDROGENATION WITH PARTICULAR CATALYSTS

In this embodiment, the second as listed above, the invention relates tocatalytic dehydrogenation of dehydrogenatable hydrocarbons, particularlyC₃ -C₁₀ alkanes, with particular catalysts which can be used in thenovel process of this invention supra, or in any dehydrogenation processwhich is conducted in the presence of added hydrogen such as the Oleflexdehydrogenation process or catalytic reforming for example. When thecatalysts of this invention are sulfided, infra, it is convenient toreplace with the catalysts of this embodiment only the last section ofcatalyst in a motor fuel reforming operation so that spilled over sulfurdoes not contaminate other sulfur sensitive catalysts such as platinumor platinum-rhenium formulations normally required for aromatization.

The dehydrogenation catalysts of this embodiment comprise combinationsof a nickel component and one or more optional modifiers as describedbelow, supported on non-acidic supports of a type which preferablyexhibit a prescribed pore structure, and activated by reduction,sulfiding with particular type of reagent, and optionally precoking. Foroptimal catalyst performance, preferred combinations and ranges of thenon-nickel (modifier) component, the pore structure of the support, thepretreatment of the support, and the method and reagents for activationof the catalysts are used, as subsequently disclosed.

The loading ranges for the nickel component can be 0.5 to 25 weightpercent nickel, preferably 2 to 12 weight % Ni, and most preferably 4 to9 weight % Ni.

In addition to a nickel component, modifier components may be added tothe catalyst. The modifier component(s) may serve the purpose ofmaintaining the dispersion of the nickel component during use, ofaltering catalyst activity or selectivity by alloying with or otherwisedirectly interacting with the supported nickel component, of adjustingthe surface acidity of an underlying metal oxide support, of gasifyingcoke which has formed as a side product during use of the catalyst fordehydrogenation, of providing an activating support layer between thenickel and bulk oxide support, or by acting as a refractory intermediatelayer which slows further reaction between the nickel and bulk oxidesupport to catalytically inactive compounds. The particular class ofmodifier which serves as an intermediate layer which hinders reaction ofsupported nickel with the underlying bulk oxide support particularlyduring use of the catalyst in a regeneration cycle in which coke isburned off, is referred to as a barrier layer, described below.

Useful modifiers are compounds or allotropes of lithium, sodium,potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium,barium, chromium, molybdenum, tungsten, copper, silver, gold, palladium,rhenium, iridium, tantalum, vanadium, iron, indium, tin, antimony, lead,bismuth, arsenic, titanium, zirconium, cerium, lanthanum, or phosphorus.Modifiers may be incorporated within the support.

The range of copper, tin or lead modifier to nickel atomic ratios usedin this embodiment of the invention is typically 1 to 80 atomic percentmodifier. The preferred range is 6 to 75 atomic % modifier; the mostpreferred range is 55 to 65 atomic % when the modifiers are Cu or Sn orSb or Bi or Pb. The limits of the ranges may vary when the modifiers areBa, Sr, Ca, Mg, Be, Li, Na, K, Rb, Cs, P or other modifiers; suitableranges may be determined by a person skilled in the art in the light ofthis specification.

Supports generally useful for this embodiment of the invention are anynon-acidic support or supports treated to reduce acidity either before,during, or after incorporation of nickel. Useful supports includeleached aluminas of reduced acidity, silicas, zirconia, titania,magnesia, chromium treated silicas or silica-titania, tantalum dopedzirconia as described in copending Durante et al application Ser. No.07/743,658 filed Aug. 12, 1991, now U.S. Pat. No. 5,221,464, issued Jun.22, 1993, the disclosure of which is hereby incorporated by reference,non-acidic forms of zeolites, such as base treated mordenite or bariumexchanged zeolite, microporous aluminum phosphates, nonacidic forms ofSAPO's (silicoaluminum phosphates), silicoferrates, silicoborates,silicotitanates, other non-acidic molecular sieves, basic clays,magnesiumaluminate spinel, zinc aluminate, carbon coated supports,ceramics, and other supports known in the art. The choice of a supportis affected in the case of our preferred compositions by a performancerange in a particular acidity test, by a favorable pore sizedistribution as specified below, and by stability to process conditions.

Physical properties such as density are also considered depending on thenature of the process reactor application. Acidity reduced,pore-modified aluminas are preferred over the molecular sieve supportsfor process conditions resulting in high coke levels between catalystregneration cycles. In cases of low temperature operation, molecularsieve or siliceous supports may be favored.

The support optionally may be pretreated not only to reduce acidity, butalso to effect a particular nickel distribution, to adjust the porestructure, as described in another embodiment infra, or to provide for asurface barrier layer which hinders reaction of the active portion ofthe nickel component with the bulk support phase during cyclicoxidation-reduction treatment or during oxidative regeneration of thecatalyst. Any suitable physical form of the support for the process inquestion may be used such as microspheres prepared by spray drying,extrudates, monoliths, beads, rings, etc.

LOW ACIDITY DEHYDROGENATION CATALYST

A required feature of the catalyst of this embodiment is low acidity.Typical transition phase alumina-based supports are too acidic fordirect use in these preparations. When aluminas are used as supports,significant reduction in acidity can be achieved by treatment of thealumina with alkali components. Reduction in surface acidity promoteslow coking rates, low hydrogenolysis rates, and, particularly lowisomerization rates.

The alkali components may be selected from the group of compounds orallotropes of cesium, rubidium, potassium, sodium, lithium, or francium,or mixtures thereof. Potassium, rubidium or cesium, or mixtures thereofare preferred alkali components. Preferably, the alkali component iswell dispersed throughout the catalyst. The addition of alkalicomponents may be accomplished by impregnation prior to or after theincorporation of nickel or in a coimpregnation step. They my also beincorporated by a coprecipitation method which often results in a mixedalumina-alkali structure after calcination in the case of aluminiceoussupports. Other methods of incorporating the alkali that may be used arecogelation and ion exchange.

We prefer to add the alkali component separately from nickel in order tonon-homogeneously distribute nickel with regard to pore structure (videinfra) yet uniformly deposit the alkali on the support surface.

The preferred alkali loading depends on the method of incorporation andthe surface area of the support, for example alumina. When using cesiumas the alkali, typically useful ranges are 1 to 8 weight percent cesiumloading. Preferred cesium loading range for a 90 m² /g precalcined andpreleached alumina (vide infra) to contain 6-8% nickel loading, is 5 to7% by weight.

In preparing zeolite supports, ion exchange or impregnation methods toremove protonic acidity are effective. Base treated mordenite or bariumion exchanged zeolite L are useful supports, for example. In the case ofbarium ion exchanged L zeolite, for example, repetitive ionexchange-calcination steps are required to reduce acidity substantially,as illustrated in Example 13 infra. After incorporation of nickel,modifier, sulfidation, and activation, sufficiently basic supportsresult in virtually no isomerization and little hydrogenolysis ofisobutane under laboratory test reaction conditions in which 2 moles ofhydrogen are cofed per mole of isobutane at 600° C. over a 10 ml bed ofcatalyst held isothermally. Further description of this aspect of theinvention is illustrated in the examples below.

The non-acidic supports employed for the catalysts of this embodimentdistinguish the same from the "bifunctional" catalysts typically used innaphtha reforming. The combination of preferred pore structures andpreferred activation methods, along with low acidity, distinguish thesecatalysts from other supported nickel catalysts known in the art forhydrocarbon conversion processes.

J. H. Sinfelt, J. Carter and D. J. C. Yates, J. Catal. (1972), 24, 283,supra, disclose the hydrogenolysis of ethane to methane and thearomatization of cyclohexane to benzene over copper-nickel alloys.

J. A. Dalmon and G. A. Martin, J. Catal. (1980), 66, 214, supra disclosehydrogenolysis of ethane, propane and n-butane over silica-supportednickel-copper alloy catalysts.

Z. Popova et al, React. Kinet. Catal. Lett. (1989), 39, 27, supra,disclose hydrogenolysis using nickel- and copper-containing catalysts.

D. Nazimek, React. Kinet. Catal. Lett. (1980), 13, 331, supra, disclosecopper admixture to the Ni/Al₂ O₃ system and the use of the resultingcatalyst in the hydrogenolysis of n-butane in the temperature range of723-573 K.

B. Coughlan et al, J. Chem. Tech. Biotechnol. (1981), 31, 593 disclosealkylation of toluene with methanol using bimetallic nickel/copperzeolite catalysts prepared from NaY and NH₄ Y as starting materials. Thecatalysts are disclosed to be ineffective for the hydrogenation ofbenzene.

S. D. Robertson et al, J. Catal. (1975), 37, 424 disclose as prior workthe oxidation of ethylene to ethylene oxide and of cumene to cumenehydroperoxide using a Ag/Au alloy catalyst, and hydrogenation ofethylene, benzene and butadiene using a Ni/Cu alloy, and as new work astudy of the reduction characteristics of copper-, nickel- andcopper-nickel-on-silica catalysts.

Although the invention in the use of a sulfided nickel catalystsupported on a non-acidic support containing optional modifiers is notto be limited by any theory of its mechanism of operation, we believethat the unwanted reaction of hydrogenolysis requires rather largeensembles of nickel to be rapid. Alloying of nickel with certainmodifiers such as copper or tin reduces the incidence of large ensemblesof nickel on the surface and acts to dilute the surface. Also hydrogenchemisorption on the surface is probably diminished relative to theunalloyed cases thereby reducing the effective hydrogen concentrationand, consequently, the rate of hydrogenolysis on the surface.Sulfidation probably further reduces the size of available nickelensembles. The lack of acidity ensures that only metallic or metalcarbide activity, as opposed to acid-catalyzed activity is observed. Thecombination of these effects results in an increase in the rate ofdehydrogenation relative to the rate of hydrogenolysis, hence in aselectivity improvement compared to a non-alloyed non-sulfided purenickel catalyst.

In the case of the use of Ta-ZrO₂ supports, it is believed that theremay be an electronic metal-support interaction which acts to suppressfurther the hydrogen chemisorption and the rate of processes such ashydrogenolysis which depend on the surface activity of hydrogen.Tantalum compounds may also assist in the gasification of coke formed asa side reaction of dehydrogenation processes.

DEHYDROGENATION CATALYST WITH SURFACE BARRIER LAYER

In addition to support acidity reduction, catalyst modifiers or, in somecases, excess nickel may be added in a separate preparation stepfollowed by calcination so as to provide for an intermediate refractorylayer between the portion of nickel component which is substantiallyactive and the bulk support, termed a barrier layer. The barrier layerserves to lessen deactivation of the finished catalyst during use or tomitigate inactivation as a result of calcination during preparativesteps by lessening bulk reaction between nickel compounds and the bulksupport oxide. The barrier layer may also serve to maintain dispersionof nickel. Preferred catalyst formulations especially on non-molecularsieve supports contain a barrier layer. Barrier layers are especiallypreferred on aluminiceous supports on which nickel aluminate mayotherwise form during calcination in air.

The formation of a barrier layer may be accomplished by treatment of thesupport prior to nickel loading with organozirconate or organotitanatereagents, preferably CAVCO MOD coupling agents sold by Cavedon ChemicalCo. or alkoxytitanates such as TYZOR reagents sold by E.I. DuPont deNemours Co., or other brand zirconium organofunctional compounds,tantalum compounds, or magnesium compounds, followed by drying andcalcination in air at conditions sufficient to convert the barrierreagents to oxides or hydroxides. This treatment can be accomplished bymethods known in the art and described in vendor literature.

Particularly with aluminiceous supports, other barrier layers may beproduced by preformation of non-nickel aluminates such as copperaluminate, on a thin layer of the support surface prior to applicationof nickel. This technique is described by Kulkarni et al. in J. Catal.131,491 (1991); the disclosure of which is incorporated herein byreference.

When a separate barrier layer is not applied to an aluminiceous support,deliberate preformation of a nickel aluminate layer may be desirable.This can be produced by repeated impregnation with nickelcompounds--calcination steps such that the first calcination is above500° C. in oxygen or air, followed by one or more subsequentimpregnation-low temperature calcination steps, followed by optionalheat treatment in reducing or inert atmospheres. Example 25 furtherdescribes this process.

On siliceous supports such as silica, silica gels, zeolites, and thelike, a preferred barrier layer is provided by incorporation ofsurface-anchored chromyl species. We believe that the surface-anchoredchromyl species provide a support environment for sulfided nickel whichresults in enhanced and longer lasting activity for alkanedehydrogenation, especially in the presence of hydrogen, than supportswithout the surface-anchored chromyl species. Without limitation to anytheory, the activity maintenance of these catalysts may be related tothe maintenance of nickel dispersion especially well in these Ni/Crcompositions with increasing time onstream. The preparation of chromylbarrier layers is readily accomplished bypretreatment of siliceoussupports with chromium compounds followed by calcination.

Chromium treated silicas and silica-titanias are known and are usedcommercially as olefin polymerization catalysts as described in M. P.McDaniel & M. B. Welsh, J. Catal. (1983) 82, 98; 110/118. Catalystsconsisting of chromia supported on aluminas without nickel are alsoknown for dehydrogenation. For example, such a catalyst is described inU.S. Pat. No. 4,746,643 (1988). Known methods of preparing surfacechromyl barrier layers according to the above articles and patents areincorporated herein by reference. Examples 7, 8, 10 and 15 through 18describe the preparation and testing of catalysts incorporating chromylbarrier layers.

CATALYST ACTIVATION

Another feature of the catalysts of this invention is their activationprior to use. The catalysts are preferably in a fully or partiallyreduced state, sulfided, and contain some amount of carbonaceousmaterial. A preferred method of activation involves the use ofcarbon-sulfur compounds such as, for example, dimethylsulfoxide, in thepresence of free hydrogen to provide the sulfur and carbon depositionrequired for activation.

Additional carbonization (coking) of the catalyst may also be conductedas part of the activation process as described infra.

These catalysts, once activated, have superior selectivity. Theyaccelerate the dehydrogenation reaction while minimizing hydrogenolysis(hydrocracking), with resulting lower loss of feedstock to unwantedreactions and in greater product hydrogen purity, and reduced unwantedproduction of methane and the like. The catalysts are reasonably sulfurtolerant and can be used on untreated refinery feeds.

Prior art disclosures of sulfided Ni catalysts for dehydrogenation are:H. E. Swift, et al., I&EC, Prod. R&D (1976). 15, 133; of Ni-Sncatalysts, V. D. Stysenko, et al., Kin. & Catal. (translation) Russianoriginal: (1987), 28, #4, Part 2, page 802, and M. Agnelli, et al.Catalysis Today (1989), g, 63; of Pt-Sn:Pt-In catalysts, Lyu Kam Lok, etal., Kinetikai Kataliz., (1988), 29, #5, 1146, and S. D. Gardner, et al.J. Catalysis, (1989), 115, 132; and of Pt-L zeolite, J. R. Bernard,Proceedings of the 5th International Conf. on Zeolites (Naples), (1980),p. 686.

CATALYSTS FOR SEVERELY DEACTIVATING CONDITIONS

In further embodiments of the invention, improvements to supportednickel catalysts render the catalysts more useful in dehydrogenationprocesses. In addition to the previously disclosed general advantages ofsulfided nickel catalysts over other known dehydrogenation catalysts,the preparations of these embodiments demonstrate additionalimprovements in performance which enable their use under what wouldordinarily be severely deactivating conditions.

Severely deactivating conditions comprise operation at temperatures ofgreater than about 530° C., at hydrogen-to-alkane feed ratios of 2 orless, and/or a requirement for more than about 90 hours on streambetween regenerations. Despite the increased rate of catalystdeactivation, operation in the severely deactivating mode is desiredbecause it results in reduced capital costs and reduced operatingexpenses in some dehydrogenation processes such as the dehydrogenationprocess previously disclosed herein, particularly as a result of thereduced volume of hydrogen which is required to be cofed. This resultsin diminished compressor load, smaller reactor volumes and easierdownstream separations.

The use of these improved catalysts in other dehydrogenation processesat operating conditions normally used for such processes results inextended catalyst life over what is typical for known catalyts.

Certain combinations of catalyst compositions and features are bettersuited than others when the catalysts are to be used under severelydeactivating conditions. Preferred formulations of catalysts result ingreater activity retention per given time-on-stream and easierregenerations, once the catalysts have been deactivated, to recoveractivity and selectivity. The preferred catalysts for use under severelydeactivating conditions may also be used at milder operating conditionssuch as at higher hydrogen-to-alkane molar feed ratios than 2.

The catalysts of this embodiment which are preferred for use underseverely deactivating conditions have one or more of the followingcharacteristics:

1) a pore size distribution of the support such that there exists agreater pore volume than a specified minimum pore volume between certain(larger) pore radius boundaries and a lesser pore volume than aspecified maximum limit between other (smaller) pore radius boundaries.This desirable overall pore structure may be achieved by a process ofleaching and calcining the support phase when the support is alumina asdescribed in a separate embodiment of the invention, infra.

2) reduced acidity achieved by doping the support with specific agentsas described above.

3) optionally, a nickel distribution on the support favoring depositionin the larger pore radius region achieved by impregnating the supportwith a temporary pore filling agent.

4) optionally, a barrier treatment which hinders additional reactionbetween nickel and bulk support during the catalyst regeneration processsuch as to form nickel aluminate and hence stabilizes the catalystagainst deactivation by reaction of the nickel with the support.

5) activation of the catalyst achieved by hydrogen reduction, sulfidingwith a reagent containing both sulfur and carbon species, and precokingof the catalyst by forming a carbonaceous layer prior to running understeady state conditions.

6) activation of the catalyst by depositing coke or other organiccompounds on a pore-modified support prior to addition of nickel andprior to hydrogen reduction, as described later in a separate embodimentof the invention.

The advantages of the novel preparations of these embodiments include:

1) greater activity retention per given time on-stream at low hydrogento isobutane feed ratios (0.1-2 mol/mol) over catalysts previousdisclosed

2) less susceptibility to pore plugging by coking than catalystspreviously disclosed

3) lowered tendency towards feed isomerization, hence improvedselectivity

4) ease of regeneration, once the catalysts are deactivated, to recoveractivity, selectivity and useful pore structure.

The inventions of these embodiments are the methods of making thecatalysts, the process for use of these catalysts for dehydrogenation oroxidative dehydrogenation of alkanes, and in the case of precokedsupports as subsequently disclosed, the composition of matter of thecatalyst.

To realize optimal benefit from the catalysts of these embodiments ofthe invention, the temperature is preferably between 550° and 630° C.but other temperatures are also operative. Although a wide range of feedcompositions can be used to advantage, a particular range of H₂/isobutane molar feed ratio, 0.3-0.5, may unobviously result in thelargest ratio of initial dehydrogenation rate to average deactivationrate when isobutane is the feed hydrocarbon.

Various support compositions can be used as previously described herein,as well as formed clays and clay derivatives, mixed metal oxides,sintered ceramics, zeolites, etc., but a preferred support because ofits ability to be modified, its stability in use, and ready availabilityand minimal cost is alumina in one of several phases. Our poremodification procedure described below is specific for alumina, butother supports can be modified utilizing the same principles but undersomewhat modified leaching and calcination conditions within the skillof the art in the light of the disclosure herein. Furthermore, variousmacroscopic forms can be utilized such as spray-dried microspheres,extruded cylinders, spherical particles formed by the oil drop method,etc., depending upon the application.

PORE SIZE DISTRIBUTION OF CATALYST SUPPORT

Of importance in preparing catalysts with long lives under severelydeactivating conditions (T>550 C; H₂ /hydrocarbon <2), is thedistribution of pores in the support in the range 10 to 600 angstromsequivalent pore radii as measured by dynamic nitrogen desorptionporosimetry and calculated assuming cylindrical pores. Since cokepreferentially deposits in the region 20 to 40 angstrom pore radii, thisembodiment of the invention minimizes the concentration of sulfidednickel component in pores in this size range. On the other hand, thisembodiment increases porosity in the radius range of 50 to 200angstroms, since this region still contributes significantly to surfacearea, yet is not as susceptible to pore blockage by coke. Porosity inpore radii greater than about 200 angstroms does not significantlyenhance performance and may lead to a physical weakening of thestructural integrity of the formed particles. Preferable porosities are:

    ______________________________________                                        Radius Range (Angstroms)                                                                           Pore Volume (ml/g)                                       ______________________________________                                        20 to 50             less than about 0.1                                      50 to 200            0.30 to 1.50                                             ______________________________________                                    

Most preferable porosity ranges are:

    ______________________________________                                        Radius Range (Angstroms)                                                                           Pore Volume (ml/g)                                       ______________________________________                                        20 to 50             less than 0.05                                           50 to 200            0.40 to 0.80                                             ______________________________________                                    

Catalysts previously described based on zeolite supports, such assulfided Ni/Cr/Ba-L zeolite, have non-optimal pore structures in theabove ranges and are inferior to the pore-modified catalysts underseverely deactivating conditions with regard to their useful on-streamlives.

FIGS. 2 and 3 of the drawings illustrate the different behavior of thetwo catalyst series. The pore volume diminution due to comparableamounts of coke deposition (about 1% by weight) is much more pronouncedfor the Ni-Cr/Ba L zeolite catalysts of FIG. 2 than for the preferredcatalyst series with preferred pore structure of FIG. 3.

The improved tolerance to coke deposition of the new catalyst series ascompared to the Ni/Cr/Ba-L catalyst series is illustrated in FIG. 4. Thezeolite supported catalysts lose pore volume by the deposition ofrelatively small amounts of coke, while the new modified aluminasupported catalysts tolerate much higher amounts of coke.

FIG. 5 is a comparison of relative activity loss in a dehydrogenationtest reactor resulting from pore volume loss due to coking for aNi-Cr/Ba-L non-pore size adjusted catalyst compared to a Ni-Cs modifiedalumina catalyst. The superior tolerance to coke of the latter catalystis evident.

These figures indicate that certain pore size distributions affect theability of supported nickel dehydrogenation catalysts to resist poreplugging and corresponding deactivation.

To further maintain activity, under severely deactivating conditions,catalysts having preferred pore structures may be loaded with nickel, ornickel plus modifier, such that there is a preferential deposition inthe larger pore size regions. This is accomplished by temporarilyfilling the smaller pores with an organic liquid which is immisciblewith or only slightly soluble in the impregnating solvent containing thenickel compound to be deposited. This is followed by impregnation with anickel solution, drying and calcination steps. This preparation methodand a resulting catalyst are further described in example 24 infra.

PRECOKING OF CATALYST

Following addition of the nickel component and modifier, the preferredcatalysts of this embodiment of the invention are activated. We havepreviously described methods and reagents for reduction and presulfidingof the nickel which are effective to achieve suitable activities andselectivities. These steps are often accomplished in-situ once thecatalyst has been installed in the reactor for the first time or after aregeneration cycle. In an improvement to this procedure, although cokeformation leads ultimately to catalyst deactivation, a small amount ofcoke deposited onto the catalyst increases the activity of the catalyst.Hence, a precoking step activates the catalyst.

For example, FIG. 10 shows an induction period to optimal catalystactivity, the delay corresponding to the buildup of a carbonaceous layeron the surface, during a fixed bed dehydrogenation reaction ofisobutane. This induction period suggests that the carbonaceous depositsactively participate in the catalytic cycle.

Precarbonization can be accomplished prior to hydrogen reduction andsulfiding either with normal feed or with other compounds such as C₃ toC₅ olefins such as isobutene, for example. Coke levels of 1 to 4 weightpercent on the catalyst are generally required for optimal activation ofour preferred catalysts for use under severely deactivating conditions.Additional coking may lead to catalyst deactivation.

Catalysts having preferred features perform well in life tests underseverely deactivating conditions of alkane dehydrogenation. Descriptionsof such tests and comparative test results are shown in Examples 21through 23.

MODIFIED PORE STRUCTURE BY LEACHING OF METAL OXIDE DEHYDROGENATIONCATALYST SUPPORTS

The third embodiment as listed supra of our invention is a technique forimproving formed transitional phase alumina and other similar metaloxide support phases such that the resulting treated solid oxide phaseexhibits a pore size distribution in the preferred range for sulfidednon-acidic nickel dehydrogenation catalysts used under severelydeactivating conditions, as described supra. The resulting phase is ofsomewhat reduced BET surface area than the starting phase but exhibitsenhanced porosity (increase pore volume) in the 50 to 200 angstromradius range and reduced porosity (lower pore volume) in the 20-50angstrom pore radius range, assuming cylindrical pores. The aluminaphase is dispersed in hot aqueous solution containing dissolveddicarboxylic acids such as oxalic acid with stirring for a timesufficient to develop increased porosity in the solid in the 50-200angstrom range, followed by washing and drying and calcining asdescribed below.

Although a number of carboxylic and dicarboxylic acids may be used,succinic acid and malonic acid are preferred reagents to selectivelydissolve alumina in the preferred porosity region. Oxalic acid my alsobe used but is not preferred. Diacids containing more than 6 carbonatoms are less favorable but may be used with some modification of time,temperature, and concentration conditions compared to preferredreagents. Any transitional phase alumina or other metal oxides which aresomewhat soluble in solutions of carboxylic acids may be used. Boehmite,gamma, eta, chi, or theta phase aluminas or bauxite may be used asshaped bodies, but alpha phase alumina is sufficiently insoluble forthis technique not to be useful.

After leaching, filtering, washing, and drying, the resulting solids arecalcined to reduce microporosity. Useful calcination temperatures arebetween 700°-1100° C. for a time sufficient to reduce microporosity.Example 19 infra further illustrates the preparative method of thisembodiment.

FIGS. 6 and 7 of the drawings illustrate the effects of calcination andleaching with oxalic acid on the pore structure of the alumina support.FIG. 6 shows the alteration in pore size distribution of gamma-aluminaby calcination at 1080° C. A clear decrease in the smaller pore range isobserved. FIG. 7 shows the combined effect of leaching and calcination.In this case, both a decrease in the 10-50 angstrom region and anincrease in the 50-200 angstrom region are clearly evident.

CATALYST CONTAINING A CARBONACEOUS LAYER BETWEEN THE SUPPORT AND THECATALYTIC METAL

In the fourth embodiment as listed supra of our invention, describedearlier, in use of sulfided nickel catalyst on non-acidic supports fordehydrogenation catalysts, carbonization can result in catalystactivation. Use of typical carbonaceous supports available commercially,as substrates for non-acidic sulfided nickel results in catalysts whichshow significant initial activity but decay quickly under the severelydeactivating conditions described earlier. In another embodiment of theinvention, a novel composition of matter is provided which hasparticular utility as an effective and long-lived hydrocarbondehydrogenation catalyst under severely deactivating conditions. Thiscomposition has catalytic utility in other processes as well, includingselective hydrogenation, hydrodesulfurization, and other conversionprocesses. The composition according to this embodiment comprises anamorphous carbonaceous layer on a porous substratum metal oxide having aparticular pore size distribution. A top layer above the carbonaceouslayer contains nickel plus modifier components.

The unique composition of this embodiment of the invention consists ofsuperimposed strata on a pore modified support which have been laid downin a particular order. The substratum support consists of a porous metaloxide, preferably aluminum oxide, in the form of powder or of a formedbody such as a honeycomb monolith, for example, with a particular poresize distribution. The particular pore volumes of the substratumsupporting metal oxide are less than 0.1 milliliter per gram of metaloxide volume in the equivalent pore radius range of 20 to 50 angstroms,calculated from a nitrogen desorption isotherm assuming cylindricallyshaped pores, and 0.25 to 1.6 milliliters per gram of metal oxide in theequivalent pore radius range of 50 to 200 angstrom pores, calculated asabove. Although a number of metal oxides may be used, slightly acidicoxide surfaces that have been leached according to another embodiment ofthis invention to produce desirable porosity, are favored. The bulkoxide may contain minor amounts of modifier components. The substratumoxide of appropriate pore volume distribution, described above, iscoated with a carbonaceous layer by any known means, preferably bythermal pyrolysis of a hydrocarbon gas, so as to produce a compositewith generally 0.2 to about 6 weight percent carbon, preferably 0.4 to 4weight percent carbon, or most preferably 1.5 to 2.5 weight percentcarbon. The carbonaceous layer may also contain some hydrogen and oxygenbut the hydrogen to carbon atomic ratio is preferably less than 0.2, andthe oxygen to carbon ratio is preferably 0.001 to 0.16 atomic ratio.Other atomic components such as for example phosphorus, sulfur, orhalogen atoms in the carbonaceous layer may be present in minor amounts,but are not preferred.

Although any suitable preparation method may be used, the amorphouscarbonaceous layer may be applied to the metal oxide substratum ofappropriate pore structure by thermal pyrolysis of a vaporized stream ofa C₃ to C₅ alkene such as isobutene over the solid at temperatures of700° to 800° C., for example. Additional thermal pyrolysis of thecarbonized solid under a flowing nitrogen atmosphere without feedingadditional hydrocarbon may be conducted to reduce the hydrogen to carbonratio to the prescribed levels. The top stratum of the compositeconsists of a sulfided nickel component plus optional modifiers suchthat the overall nickel loading in the layered composite is in the rangeof 0.5 to 25 weight percent nickel, or preferably in the range of 2 to12 weight percent nickel, or most preferably in the range of 4 to 9weight percent nickel. The optional modifier component may be chosenfrom the modifiers of nickel dehydrogenation catalysts described inother embodiments of this invention. The nickel may be applied by anyknown technique, for example, by impregnation of the evacuatedcarbonized substratum to incipient wetness using a solution of nickelnitrate in acetone solvent. After solvent evaporation, thenickel-containing solid may be pyrolyzed under nitrogen at 500° C.followed by reduction under flowing hydrogen at 400° C. for 16 hoursfollowed by sulfiding with a dimethylsulfoxide/hydrogen mixture attemperatures sufficient to decompose the dimethylsulfoxide. Prior to thesulfiding step, optional modifiers such as a cesium component or a tincomponent may be applied, preferably using non-aqueous solutions ofreagents to impregnate the composite.

The novel compositions of this embodiment of the invention areparticularly suitable catalysts for the selective dehydrogenation ofdehydrogenable organic compounds under severely deactivatingdehydrogenation conditions. Although the invention is not to be limitedby any theory of operation, catalysts of our novel compositions featurea large number of sites of organometal species (interface sites betweennickel and hydrogenatable organic moieties) which we believe to be theactive site in the working catalyst (resulting in high activity) butpocketed in a pore structure which promotes a low deactivation rate(resulting in long life on-stream).

Compositions consisting of nickel deposited onto a carbonaceous supportfollowed by reduction and sulfiding differ from our novel compositionsin that pure carbon-type supports do not typically contain the largepore structures appropriate for long life. These known catalysts havehigh initial activities, but decay quickly. Our novel catalysts of thisembodiment, on the other hand, have the appropriate carbon-nickelinteraction for high activity yet maintain high activity substantiallylonger than nickel on uniform carbon supports, particularly underseverely deactivating dehydrogenation conditions.

CATALYST FOR SELECTIVE HYDROGEN OXIDATION

In the fifth embodiment as listed supra, the invention relates to thepreparation and use of a catalyst which selectively promotes hydrogencombustion while minimizing combustion of desirable hydrocarbon. Thecatalyst can be used in connection with the dehydrogenation processesdisclosed herein, as well as in other processes involving selectiveoxidation of hydrogen such as those disclosed in U.S. Pat. Nos.4,435,607 and 4,788,371.

The catalyst used in this embodiment of this invention is a metalphosphate, preferable a phosphate of a metal in Group IVb or Vb and morepreferably a phosphate of tin. These compounds are known in the priorart; see for example U.S. Pat. No. 4,252,680. Other Group IVb or Vbmetals may be used, for example, bismuth.

To use the catalysts of this embodiment, a mixture of hydrogen andhydrocarbons is contacted with the catalyst and an oxygen-containing gasat hydrogen oxidation conditions, to allow hydrogen and oxygen to react,and a reaction product mixture containing water in the form of steam andunreacted hydrocarbons is removed from the reaction zone. Alternatively,pure hydrogen or a dilute hydrogen stream in an inert carrier may beused. Preferred conditions are temperatures in the range from 430° to600° C., pressures in the range from 0 to 50 psig and space velocitiesin the range from 5,000 h⁻¹ to 40,000 h⁻¹. Preferably, the amount ofoxygen used is in the range from 0.5 to 1.1 moles of oxygen per mole ofhydrogen burned.

The catalyst used may be in the form of a bed of granular solids.Alternatively, it may be coated on a porous honeycomb monolithic supportas shown in FIG. 14 of the drawings. Use of the catalyst on thestructure of FIG. 14 prevents bulk mixing of oxygen and hydrocarbons andhydrogen except at the interface over the selective catalyst. Tomitigate migration of tin compounds off of the catalyst at hightemperature, a pretreatment step may be performed with hydrogen at about600° C. as a final step of catalyst preparation to remove excessiveamount of tin prior to use.

In addition to Group IVB or Group VB compounds, minor amounts of iron,manganese, or chromium salts may be added to the catalyst during thegelling stage as combustion initiators for low temperature service,preferably when the catalyst is to be used below about 500° C. Thepressure of the oxygen stream is slightly higher than that of thehydrogen/hydrocarbon stream, preferably within the range of 1.1 to 2times higher.

The monolith structure of FIG. 14 can also be used in the catalyticdehydrogenation processes disclosed herein, the dehydrogenation catalystbeing coated on the support in the manner illustrated in FIG. 14 for theoxidation catalyst.

Example 28 infra illustrates this embodiment of the invention.

MULTI-STEP PROCESS FOR DEHYDROGENATION USING PARTICULAR CATALYSTS FORTHE DEHYDROGENATION SECTION

This embodiment is a process for dehydrogenation of dehydrogenatablehydrocarbons using a combination of the general process scheme describedin an earlier embodiment along with the dehydrogenation catalysts ofthis invention described in other embodiments. Any hydrogen combustioncatalyst may be used of sufficient activity and selectivity. A narrowerrange of process operating conditions than in the more generalembodiment results in favorable process economics and good catalystperformance. The dehydrogenation catalysts used in this embodiment aresulfided nickel on non-acidic pore-modified supports and the operatingconditions in this embodiment are as described in other embodiements,with the exceptions noted below.

Once the catalysts have been installed, sulfided and activated in areactor, as previously described herein, hydrocarbon feed is introducedalong with hydrogen as previously described. Surprisingly, there is anoptimal ratio of hydrogen to hydrocarbon feed for best catalystperformance. Catalyst performance is measured by computing the ratio ofinitial dehydrogenation rate to average deactivation rate as a functionof hydrogen to hydrocarbon ratio at a given operating temperature, say600 degrees C., operation. The greater this merit ratio, the better theperformance. When the feed is isobutane, the optimum ratio of hydrogento isobutane is between about 0.3 to 0.5, as shown in FIG. 13 of thedrawings. Other hydrocarbon feed components show optima differingslightly from that of isobutane.

Under typical operation at these optimal conditions, the catalystsdescribed herein will eventually lose activity. We believe that areasonable cycle length is governed by the time it takes to build up10-15% weight coke as measured by LECO carbon analysis, that is, thetime to just fill the large pores of the preferred catalyst formulationwith coke or slightly lesser time. Regeneration can then be easilyaccomplished by feeding air or diluted air or oxygen over the catalystat 400° to 600° C., preferably 440° to 490° C., for a time sufficient tocombust a portion of, but not all of the coke. Optimally, 0.5-1.0 weightpercent coke may be left on the catalyst after the regeneration cycle,but values as low as 0.02 weight percent may be tolerated. Typicalregeneration times under air or oxygen at 600° C. are 0.5 to 6 hours,but the exact time depends on the level of carbon burnoff to be achievedand on the feed rate of oxygen-containing gas. Catalysts containing abarrier layer generally require a lower temperature, for example, lessthan about 500° C., for regeneration, than that required for catalystsnot containing a barrier layer. After burnoff, the catalyst is reducedand resulfided and optionally further activated by allowing coke tobuild to optimal levels prior to resumption of the dehydrogenation step.The sulfiding and reduction may be done concurrently with the early partof the subsequent dehydrogenation step.

DETAILED DESCRIPTION OF MULTI-STEP PROCESS

The multi-step process of one embodiment of the invention will befurther described with reference to FIG. 1, which is a schematic diagramof a typical process flow according to the invention:

Butanes and hydrogen are introduced into zoned adiabatic reactor 10through line 12, and contacted in reactor 10 with a bed 14 of granulardehydrogenation catalyst. Butanes in the feed are dehydrogenated to formbutenes and additional hydrogen, which pass upwardly together withunreacted butanes into bed 16 of granular catalyst for the selectiveoxidation of hydrogen to water. Because of the endothermic nature of thedehydrogenation reaction, the reaction mixture undergoes a reduction intemperature between the point of entry into the bed 14 and the point ofentry from bed 14 into bed 16. In bed 16, a portion of the hydrogen isselectively oxidized, leaving the hydrocarbons mainly unoxidized, andgenerating heat which raises the temperature of the reaction mixture toprepare the mixture for the second dehydrogenation catalyst bed 18. Inbed 18, previously unreacted butane is dehydrogenated to form additionalbutene and hydrogen, the reaction mixture undergoing another reductionin temperature in the process. The reaction product mixture passes frombed 18 into bed 20, wherein a portion of the hydrogen produced in bed 18is selectively oxidized to form water and generate heat which preparesthe reaction mixture for the third dehydrogenation catalyst bed 22. Inbed 22, previously unreacted butanes are dehydrogenated to formadditional hydrogen and butenes product. The reaction product mixture isremoved from reaction vessel 10 through line 24, then is passed throughindirect heat exchange with fresh and recycle butane feed introducedinto heat exchanger 26 through line 28. The product mixture is thenintroduced into condenser 29 wherein water is condensed from the mixtureand removed through line 30. The uncondensed product mixture is thenpassed into hydrogen-selective membrane separator 32 through line 34.Butane/butene product is removed through line 36 to butane/buteneseparation not shown. Net hydrogen production from the process isremoved through line 38, and hydrogen recycle is passed through lines 40and 12 into reactor 10. Heated fresh and recycle butane feed isintroduced into reactor 10 through lines 42 and 12.

Catalysts used for dehydrogenation according to the embodiments of theinvention, require sulfidation for optimum performance. Sulfidation maybe done prior to loading catalyst in the reactor and/or may be done byadding a sulfur-containing material to the reactants, as through line 44in FIG. 1, or other suitable point of introduction. In some cases atleast, even though the catalysts are presulfided, additional sulfur isneeded in order to maintain catalyst selectivity.

Steam may optionally be employed in the process according to theinvention, through line 44 or at other suitable point of introduction.

MULTI STEP PROCESS FOR DEHYDROGENATION USING PARTICULAR CATALYSTS FORTHE DEHYDROGENATION SECTION AND PARTICULAR CATALYSTS FOR THE HYDROGENCOMBUSTION SECTION

In this seventh embodiment listed supra, sulfided nickel on nonacidicsupport or sulfided nickel and carbon on a large pore alumina support isused as dehydrogenation catalyst, and tin phosphate, for example, isused as selective hydrogen combustion catalyst in the multiple stepprocess, all as previously described.

EXAMPLES OF CATALYTIC DEHYDROGENATION WITH PARTICULAR CATALYSTS

The invention will be further described in connection with the followingexamples:

In Examples 1 through 6, catalysts according to the invention containingzeolitic supports were tested for dehydrogenation of normal butane andcompared to the performance of the catalyst of U.S. Pat. No. 4,727,216(prepared according to the patent directions) in the presence ofhydrogen after sulfiding.

EXAMPLE 1

The catalyst according to U.S. Pat. No. 4,727,216 was prepared asfollows: ELZ-L Mol Sieve manufactured by Union Carbide Corporation,1/16" extrudate, was ground and sieved to 18/35 mesh. The zeolite wasexchanged three times with hot 0.21 molar barium nitrate solution, withcalcination between exchanges washed with hot deionized water, and driedat 125° C. The dried catalyst was calcined in a muffle at 590° C. for2.0 hours. The zeolite was impregnated to incipient wetness with asolution of tetraamine platinum nitrate and dried in a 125° C. oven. Itwas calcined in a muffle programmed to heat at 3C/minute to 260° C. andhold at 260° C. for 2.0 hours. The catalyst was then transferred to atube furnace and heated in flowing hydrogen at 482° C. for 1.0 hour. Thecatalyst was impregnated by incipient wetness with a pentane solution oftributyl tin chloride, after which the solvent was allowed to weatheroff at room temperature. It was then heated in flowing air at 482° C.for 1.2 hours, followed by flowing hydrogen at 482° C. for 2.0 hours.After the hydrogen treatment, the catalyst was treated with 3 percenthydrogen sulfide in hydrogen at 482° C. for 15 minutes. Furthersulfiding was conducted in the reactor. The finished catalyst wasanalyzed by atomic adsorption and found to contain 0.99% Pt, 0.45% Snand 7.3% Ba after appropriate dissolution. Analysis for sulfur wasinconclusive.

EXAMPLE 2

A Ni-Sn-Ba L zeolite catalyst according to the invention was prepared asfollows. A portion of ELZ-L Mol Sieve, 18/35 mesh, was exchanged twicewith hot 0.23 molar barium nitrate solution, dried at 125° C., andcalcined in a muffle at 590° C. for 2.0 hours. The zeolite wasimpregnated by incipient wetness with a solution of nickel nitratehexahydrate, dried at 125° C. and heated in a tube furnace in flowingair at 260° C. for 1.5 hours, followed by treatment with flowinghydrogen at 420°-550° C. for 1.5 hours. The catalyst was impregnated toincipient wetness with a pentane solution of tributyl tin chloride,after which the solvent was allowed to weather off. The catalyst wasthen calcined at 560° C. in flowing air for 1.0 hour, and heated inflowing hydrogen sulfide/hydrogen (5% H₂ S) at 482° C. for 1.0 hour. Thefinished catalyst was analyzed by atomic absorption to contain 0.23% Ni,0.56% Sn, and 6.04% Ba after appropriate dissolution.

EXAMPLE 3

A Ni-Sn-Na-S mordenite catalyst according to the invention was preparedas follows. Hydrogen mordenite (Norton H-Zeolon) was exchangedsuccessively with 0.05M NaOH at 70° C. and finally with 0.75M NaOH at65° C. The exchanged mordenite was dried at 125° C. and slurried withenough colloidal silica (Nyacol 30% SiO₂ manufactured by PQ Corp.) togive 18 percent silica on the finished catalyst. After drying at 125°C., the bound mordenite was ground and sieved to 18/35 mesh. A portionof the mordenite granules was impregnated to incipient wetness with asolution of nickel nitrate hexahydrate and dried at 125° C. The catalystwas calcined at 590° C. for 2.0 hours, followed by treatment withflowing hydrogen at 482° C. for 1.0 hour. The reduced catalyst wasexposed to air at room temperature, and impregnated with a pentanesolution of tributyl tin chloride. The solvent was allowed to weatheroff at room temperature, after which the catalyst was calcined at 482°C. for 1.0 hour. A portion of the calcined catalyst was treated with aflowing stream of 5 percent hydrogen sulfide in hydrogen at 482° C. for1.0 hour. Analysis of the finished catalyst indicated it contained 0.96%Ni, 1.90% Sn, and 3.75% Na. Prior to testing, this catalyst was sulfidedfurther by passing 500 ppm H₂ S in H₂ over it at about 450° C. for 0.5hour followed by pure hydrogen for 15 minutes.

EXAMPLE 4

The catalyst of Example 3 was given a further sulfiding and reductiontreatment in the reactor by passing 500 ppm H₂ S in hydrogen over it atabout 590° C. for 45 minutes followed by pure hydrogen for fifteenminutes.

EXAMPLE 5

A portion of the sodium-exchanged mordenite granules from thepreparation of Example 3 was exchanged with a hot 0.034M solution ofnickel nitrate hexahydrate and washed with hot deionized water. Theimpregnated catalyst was dried overnight at 95° C. and later impregnatedby incipient wetness with a solution of copper(II) nitratehemipentahydrate. After drying at 125° C., the impregnated catalyst washeated in flowing hydrogen at 450° C. for 2.0 hours. Analysis of thecatalyst indicated it contained 1.40% Ni and 3.75% Na. Prior to testing,the catalyst was reduced by flowing hydrogen over it while thetemperature was raised at 5°/min up to 590° where it was held for 10minutes prior to switching to the test feed solution.

EXAMPLE 6

A portion of the catalyst prepared according to Example 5 was sulfidedfollowed by pure hydrogen treatement in the reactor by the sameprocedure described above for the preparation of the catalyst of Example4.

The tests on the above catalysts of Examples 1 through 6 were conductedin an isothermal downflow packed bed, quartz, computer-supervisedreactor equipped with on-line multidimensional GC analytical capabilityand with a quadrupole mass spectrometer which could sample the fullstream composition and which featured low ionization voltage capabilityto determine molecular ions. The GC system was calibrated againstcommercial mixtures of the expected hydrocarbon products and againstinternal compositions generated by mass flow controllers which in turnhad been calibrated against a wet test meter certified traceable to theNational Bureau of Standards. The continuously operating MS detector wasused to monitor compositional trend changes between samples taken foron-line GC analyses. The catalysts were each prereduced under flowinghydrogen followed by sulfiding with 500 ppm H₂ S in H₂ (off-line) forone hour at up to 590° C. followed by further treatment with purehydrogen after which time they were brought to reaction temperature andthe feed changed to 6:1 hydrogen to butane at the specified GHSV.Internal temperature was monitored by a thermocouple inserted into thebottom third of the catalyst bed; pressure was controlled by automaticfeedback loop back pressure regulator at 39+2 psig and flow by acombination of mass flow controllers and an HPLC metering pump forliquid butane. Normal butane was vaporized and mixed with hydrogen priorto the reactor. No data were taken for one hour to allow steady state tobe achieved, then data were taken at 2 hour intervals thereafter for atleast 12 hours. No further sulfur was added in these tests after theinitial treatment of the catalyst.

The results of these tests are summarized in Table I. A few runs showedhigher conversions than equilibrium conversion due to a contribution ofunselective conversion to generate hydrogenolysis products such asmethane, ethane, propane, propene, or ethene, grouped under the headingC₃₋ in the table. Thus, high conversions are undesirable when due topoor selectivity. No butadiene was detected in any run in other thantrace quantities. Isobutane yield, resulting from isomerization of thenormal butane feed, is not reported, but is minor. The preferredcatalysts for use according to the invention minimize isomerization.

                                      TABLE I                                     __________________________________________________________________________    COMPARISON OF CATALYST PERFORMANCE FOR n-BUTANE DEHYDROGENATION               IN THE PRESENCE OF HYDROGEN                                                   (C.sub.4 GHSV = 500 h, H.sub.2 GHSV = 3000 h, Packed Bed Reactor)                        TEMP                                                                              TIME                                                                              C.sub.4 CONV.                                                                      SELEC. C.sub.4 ═                                                                 SELEC. C.sub.3 --                                                                    YIELD C.sub.4 ═                     CATALYST   (°C.)                                                                      (HRS)                                                                             (MOL %)                                                                            (C MOL %)                                                                            (C MOL %)                                                                            (MOL %)                                 __________________________________________________________________________    A.                                                                              Example 1                                                                              590 1-12                                                                              46.9 ± 1.9                                                                      38.5 ± 1.2                                                                        50.2 ± 1.2                                                                        18.1                                      Pt/Sn/Ba--L zeol/S                                                          B.                                                                              Example 2                                                                              584 1-12                                                                               7.6 ± 1.3                                                                      58.1 ± 1.1                                                                        31.2 ± 0.5                                                                        2.4                                       Ni/Sn/Ba--L zeol/S                                                          C.                                                                              Example 3                                                                              592 1   8.2  54.8   33.7                                             Ni/Sn/mordenite/S                                                                          3   9    68.8   31.2   6.2                                       (low severity S)                                                                           12  10   62     38     6.2                                       (0.97 wt % Ni,                                                                1.90 wt % Sn, VF)                                                           D.                                                                              Example 4                                                                              590 1   6.0  64.5   35.5   3.8                                       Ni/Sn/mordenite/S                                                                          6   7.8  61.8   38.2   4.8                                       (high severity S)                                                                          12  9.2  61.2   38.8   5.6                                     E.                                                                              Example 5                                                                              628 1   100  0      100    0                                         Ni/Cu/mordenite                                                                        613 3   86.1 0      100    0                                         not sulfided                                                                           602 12  66.0 3.2    96.8   2.1                                                587 1   66.4 4.2    95.8   2.8                                                560 1   64.6 1.5    98.5   1                                       F.                                                                              Example 6                                                                              591 1   14.3 61.2   31.2   8.7                                       Ni/Cu/mordenite/S                                                                          3   23.0 66.3   33.7   15.2                                      (high nickel)                                                                              6   25.9 38.0   42.0   15.0                                                   9   27.0 52.2   47.8   14.1                                                   12  28.6 47.5   43.8   13.6                                    __________________________________________________________________________

Comparing the first two lines of the table, one finds that at equivalentmolar loading in Ba-L zeolite, nickel was less active but more selectivethan Pt after H₂ S sulfiding. The Pt catalyst was of the composition ofthe 216 patent supra. Without sulfiding, the Ni/Cu alloy catalystseverely destroyed butane to hydrogenolysis. The selectivity performanceof the Ni/Cu composition shown decayed somewhat with time, the yield ofbutenes going through a maximum. We believe this was due to the loss ofsulfur from the catalyst with the time on-stream and that this catalystwould fare better in a reactor in which sulfur was continuously fed orafter sulfiding with the preferred reagents.

EXAMPLES OF NICKEL-CHROMIUM DEHYDROGENATION CATALYST COMPOSITIONS

Catalysts of the type described supra containing nickel and chromiumwere prepared and compared to controls in which one of the essentialcomponents was missing, either the chromium, the nickel or thesulfiding. Testing was conducted in a manner described previously in acomputer supervisory controlled quartz, packed-bed reactor with on-lineanalytical capability after sulfiding with 500 ppm H₂ S in H₂ followedby pure hydrogen treatment to remove excess H₂ S.

All catalysts described below were sulfided and re-reduced just beforeuse in the test reactor system with 500 ppm H₂ S/H₂ for one hour at450°-590° C. followed by H₂ treatment at 590° C.

The silica used was PQ CS-1231, Lot No. 994-8601, 335 m² /g, pore volume+1.25 ml/g, 18/35 mesh, dried at 125° C.

EXAMPLE 7 Nickel Oxide on Chromia/Silica

1.93 g. chromium trioxide, CrO₃, was dissolved in deionized water togive a 50 ml solution. This solution was used to impregnate 50.2 g. ofsilica to incipient wetness. Dried overnight in 125° C. oven. A portionof the catalyst was put in a bottle and saved. The remainder was heatedin flowing air at 540° C. for one hour. 28.7 g. of the calcined catalystwere impregnated with 32 ml of aqueous solution containing 4.22 g.nickel nitrate hexahydrate. Dried for two days in 125° C. oven, andheated in flowing air at 540° C. for several hours. Cooled to roomtemperature. Heated in flowing hydrogen at 450° C. for 2 hours. Expected2% Cr, 3% Ni. Found 1.83% Cr, 2.54% Ni.

EXAMPLE 8 Nickel Oxide on Chromia/Silica

A portion of the chromia/silica produced as described below was heatedin flowing air at 540° C. for one hour. 20.4 g. of the chromia/silicawere impregnated with 24 ml of an aqueous solution containing 3.01 g. ofnickel nitrate hexahydrate. Dried overnight in 125° C. oven. Heated inflowing hydrogen to 450° C. and held at 450° C. in flowing hydrogen for2 hours. Expected 1.0% Cr, 2.9% Ni. Found 1.04% Cr, 2.64% Ni.

EXAMPLE 9 Chromia/Silica

50 g. of silica were impregnated with 53 ml of aqueous solutioncontaining 1.03 g. chromium trioxide. Dried overnight in 125° C. oven.

EXAMPLE 10 Ni+Sn on Chromia/Silica

16.8 g. of the H₂ -treated Ni/Cr/silica prepared as described above,were impregnated with 20 ml of a benzene solution containing 2.47 g. oftetrabutyl tin, Aldrich.

The impregnated catalyst was allowed to stand wet for three days, afterwhich the benzene was allowed to weather off in the hood. The catalystwas heated slowly in flowing nitrogen to 300° C. and held at 300° C. forone hour, then cooled, the flow changed to hydrogen, and heated to 450°C. The catalyst was then held at 450° C. in flowing hydrogen for 1.5hours. Expected 5% Sn. Found 3.33% Sn.

EXAMPLE 11 Chromia/Silica

30 g. of silica were impregnated with 32 ml of aqueous solutioncontaining 2.5 g. of chromium trioxide, then dried overnight in 125° C.oven, heated in flowing air at 540° C. for 2 hours, and cooled to roomtemperature. The flow was changed to hydrogen and the catalyst heatedslowly to 450° C., then heated in flowing hydrogen at 450° C. for onehour.

EXAMPLE 12 Highly Dispersed Nickel on Silica

33.4 g. of silica were impregnated with 70 ml of dry acetone solutioncontaining 4.34 g. of nickel nitrate hexahydrate. The acetone wasremoved under vacuum. The catalyst was heated in flowing hydrogen to450° C. and held at 450° C. for one hour. Expected 2.6% Ni. Found 2.16%Ni.

Results of normal butane dehydrogenation appear in Table II.

                                      TABLE 11                                    __________________________________________________________________________    COMPARISON OF CATALYST PERFORMANCE FOR n-BUTANE DEHYDROGENATION               IN THE PRESENCE OF HYDROGEN (C.sub.4 GHSV = 500 h.sup.-1,                     H.sub.2 GHSV = 3000 h.sup.-1, PACKED BED REACTOR, 591 ± 1° C.,      P = 31 PSIG)                                                                                ON STREAM                                                                            C.sub.4 CONV.                                                                      SELEC. C.sub.4 ═                                                                 YIELD C.sub.4═                                                                  CH.sub.4 /C.sub.2 H.sub.6              CATALYST      TIME (Hrs.)                                                                          (MOL %)                                                                            (C MOL %)                                                                            (MOL %)                                                                             (In C.sub.3 -Prods)                    __________________________________________________________________________    1. 2.16% Ni/SiO.sub.2 /S                                                                    1      37.6 48.0   18.1  3.6                                       Example 12 3      43.8 39.8   17.4  6.3                                                  6      49.0 18.3   9.0   5.3                                                  9      51.6 19.3   10.0  16.5                                                 12     58.2 19.0   11.0  17.8                                   2. 1.94% Cr/SiO.sub.2 /S                                                                    1      41.4 32.7   13.5                                                       3      25.1 58.5   14.6                                                       6      30.9 58.2   18.0                                                       9      36.4 58.3   21.2                                                       12     24.7 59.0   14.6                                                       15     17.8 61.0   10.9                                                       18     26.0 58.9   15.3                                                       21     37.4 32.5   12.1                                                       24     36.5 32.4   11.8                                         3. 2.64% Ni/1.04%                                                                           1      100  0      0     infinity                                  Cr/SiO.sub.2 /No S                                                         4A.                                                                              2.64% Ni/1.04%                                                                           1      26.5 32.1   8.5   1.1                                       Cr/SiO.sub.2 /S                                                                          3      32.2 58.5   18.8  1.2                                       Example 8  6      13.2 63.6   8.4   0.5                                                  9      27.1 62.3   16.9  0.4                                                  12     35.1 59.3   20.8  1.2                                    4B.                                                                              RESULFIDE  1      25.2 50.3   12.7  1.2                                                  3      28.6 60.6   17.3  1.2                                                  6      17.5 64.8   11.3  0.3                                                  9      27.8 63.2   17.6  0.5                                                  12     28.4 63.1   17.9  0.4                                    5. 2.6% Ni 3.3% Sn/1.0%                                                                     1      18.9 31.0   5.9   1.2                                       Cr/SiO.sub.2 /S                                                                          3      17.1 30.9   5.3   1.2                                       Example 10 6      19.1 --     --    --                                                   9      22.4 31.0   7.0   1.2                                                  12     19.8 30.7   6.1   1.2                                    6. 1.8% Cr/2.5 Ni/                                                                          1      17.6 0      0                                               SiO.sub.2 /S                                                                             3      22.9 61.2   14.0                                            Example7   6      15.0 61.9   9.3                                                        9      27.4 59.4   16.3                                                       12     21.7 59.0   12.8                                                       15     27.7 57.5   15.9                                                       18     24.8 58.4   14.5                                                       21     25.8 57.9   14.9                                                       24     53.6 58.2   31.2                                         __________________________________________________________________________

No butadiene was detected in any of the runs of Table II.

The data in Table-II show the relatively rapid decline in selectivityand yield with increasing time on-stream over a silica-supportedcatalyst after initial sulfiding; no sulfur was cofed with butane andhydrogen. The increase in CH₄ /CH₂ H₆ ratio (Table II) correlates withdesorption of sulfur as H₂ S with time on-stream.

Chromiated silica is represented by entry 2 of Table II. Yield improvedover 9 hours, then declined over this catalyst; selectivity declinedafter about 18 hours as shown in Table II, entry 2.

Without sulfiding, only hydrogenolysis products (CH₄) were observed froma 2.6% Ni/1% Cr/SiO₂ catalyst (entry 3 of Table II). Presulfidingresulted in low methane yields (low CH₄ /C₂ H₄) and high selectivitiesand yields (entries 4A, B of Table II). These good results weresustained much longer than those of the Ni/SiO₂ /S catalyst whichcontained no chromium. When selectivity began to drop slightly after 12hours on-stream, resulfiding restored selectivity after an inductionperiod. Low CH₄ /C₂ H₆ ratios were observed after resulfiding (entry 4Bof Table II).

Another example of superior yield and selectivity of the Ni/Cr/Si₂/S-type catalysts is entry 6 of Table II.

NOVEL NICKEL CATALYSTS ON NON-ACIDIC FORMS OF ZEOLITE L

In another set of examples, novel nickel-based catalysts, optionallyalloyed with tin or indium, are supported on non-acidic forms of zeoliteL such as exhaustively barium-exchanged L zeolite. The catalysts exhibitgood selectivity for production of monoolefins without generating muchcoke or diolefins and with little hydrogenolysis product (e.g., methane)production under conditions in which hydrogen is cofed along with normalbutane at high temperature over the catalyst.

EXAMPLE 13

Catalyst was prepared as follows:

Exchanges: 53.2 g. zeolite L (Union Carbide Lot #11842-31, 16"extrudate, ground and sieved to 18/35 mesh) granules are immersed in 500ml of 0.5M barium chloride solution at 70° C. with gentle stirring for30 minutes. The solution was decanted and the zeolite washed three timesin hot deionized water. The zeolite was dried in 125° C. oven and heatedin a muffle furnace programmed to heat at 9° C./minute to 593° C. andhold for two hours. This procedure was repeated three more times using250 ml quantities of 0.5M barium chloride solution. The product waslabeled as Sample A.

Impregnation: 5.0 g. of nickel nitrate hexahydrate were dissolved in dryacetone to give 20 ml of solution. This solution was used to impregnate39.8 g. of the above zeolite by incipient wetness. The acetone wasallowed to weather off in a hood, after which it was dried in a 125° C.oven and calcined in a muffle at 400° C. for one hour. Labeled as SampleB.

Impregnation: Approximately half of Sample B, 18.3 g., was impregnatedwith 10 ml of a benzene solution containing 2.72 g. of tetrabutyltin.The impregnated zeolite was allowed to stand wet overnight, after whichit was loaded into a tube furnace and heated slowly in flowing nitrogento 300° C. The heating continued at 300° C. in flowing nitrogen for 105minutes. Labeled as Sample C.

Table III below illustrates the outstanding performance characteristicsof Ni-Sn-Ba-L catalysts for n-butane dehydrogenation under conditions inwhich hydrogen is cofed along with the alkane.

All catalysts in Table III were presulfided in-situ prior to testingwith 500 ppm H₂ S/H₂ for one hour between 450°-590° C. followed by H₂reduction.

                                      TABLE III                                   __________________________________________________________________________    COMPARISON OF CATALYST PERFORMANCE FOR n-BUTANE DEHYDROGENATION               IN THE PRESENCE OF HYDROGEN (C.sub.4 GHSV = 500 h.sup.1, H.sub.2 GHSV =       3000 h.sup.1,                                                                 PACKED BED REACTOR, 591 ± 1° C., P = 31 ± 2 PSIG)                           ON STREAM                                                                            C.sub.4 CONV.                                                                      SELEC. C.sub.4 ═                                                                 YIELD C.sub.4═                                                                  CH.sub.4 /C.sub.2 H.sub.6                 CATALYST   TIME (Hrs.)                                                                          (MOL %)                                                                            (C MOL %)                                                                            (MOL %)                                                                             (In C.sub.3 -Prods)                       __________________________________________________________________________    Pt/Sn/Ba--L zeol/S                                                                       1-12   46.9 ± 1.9                                                                      38.5 ± 2.1                                          2.16% Ni/SiO.sub.2 /S                                                                    1      37.6 48.0   18.1  3.6                                                  3      43.8 39.0   17.4  6.3                                                  6      49.0 18.3   9.0   5.3                                                  9      51.6 19.3   10.0  16.5                                                 12     58.2 19.0   11.0  17.8                                      *2.5% Ni/.sub.4 xc Ba--L                                                                 1      43.8 59.2   25.9  0.9                                                  3      53.7 43.1   23.2  2.3                                                  6      38.0 44.1   16.7  20.1                                                 9      52.3 24.1   12.6  4.0                                                  12     50.4 41.2   20.8  23.7                                      Resulfide  1      39.7 66.5   26.4  1.2                                                  3      51.1 47.7   24.4  3.8                                                  6      41.4 42.2   17.5  7.2                                                  9      51.2 40.1   20.5  9.8                                       0.72% Ni/Sn.sub.4                                                                        1      33.9 33.9   11.5  1.1                                       xc Ba--L/S 3      27.8 33.2   9.2   1.1                                       (0.61 = Sn/Ni)                                                                           6      23.3 70.4   16.4  0.3                                                  9      32.8 69.2   22.7  0.5                                                  12     37.1 68.8   25.5  0.4                                       Overnight/He/200°                                                                 1      42.6 48.5   20.6  1.2                                                  3      30.9 56.3   17.4  0.6                                                  6      31.7 55.8   17.7  0.8                                                  9      33.4 54.9   18.3  0.7                                                  15     45.5 61.5   28.0  0.5                                                  12     39.2 54.4   21.3  0.8                                                  18     40.5 54.0   21.9  0.8                                                  21     41.0 54.5   22.3  0.7                                                  24     37.5 54.0   20.3  0.8                                       Resulfide  1      36.4 48.1   17.5  1.1                                                  6      31.4 66.3   20.8  1.3                                                  12     29.4 69.4   20.4  0.4                                                  15     43.0 68.0   29.3  0.4                                                  18     43.6 68.8   30.0  0.3                                                  21     44.9 68.2   30.6  0.4                                                  24     32.8 55.3   18.2  0.6                                       2.4% Ni/2.7% Cu/K-                                                                       3-A    9.2  0      0     0.6                                       MORDEN/S   6      27.5 0      0     0.02                                      (3.68% K)  9      12.5 0      0     0.4                                                  12     25.8 0      0     0.02                                                 15     13.8 30.2   4.2   0.5                                                  18     20.4 48.8   10.0  0.3                                       Resulfide  3A     13.9 0      0     0.4                                                  6      12.6 0      0     0.3                                                  9      13.2 0      0     0.4                                                  12     24.2 0      0     1.1                                                  15     24.0 0      0     1.2                                                  18     20.7 0      0     1.1                                                  21     9.1  0      0     0.5                                                  24     12.2 0      0     0.4                                       Ni/Cu/K-Morden/S                                                                         3      12.6 0      0                                                          9      12.7 0      0                                                          15     10.0 0      0                                                          21     10.9 0      0                                                          24     9.9  0      0                                               __________________________________________________________________________     *Nominal loading; actual may be much lower.                              

Under continuously sulfiding conditions, for example, if 2 ppm H₂ S werecofed along with hydrogen and alkane over this catalyst, or by use ofour preferred sulfiding procedure, these catalysts would have longeronstream times, higher selectivity, and more stable yield behavior, asshown in later examples.

CATALYSTS SULFIDED WITH CARBONACEOUS SULFUR COMPOUNDS

In one embodiment of the invention, nickel and nickel-chromiumdehydrogenation catalysts are sulfided with particular reagents such asdimethylsulfoxide to obtain catalysts useful in the processes describedin this application, and also in other known dehydrogenation processes.

The following examples illustrate this embodiment of the invention:

Each of the catalysts prepared as described in Examples 15 through 18was sulfided using dimethylsulfoxide as sulfiding agent as describedfollowing Example 18.

Catalysts were life tested in 1/2" O. D. isothermal packed bedcontinuous reactor (17 ml catalyst) equipped with internal thermocouple,a preheater/mixer chamber, and product collection facilities. Hydrogenwas fed through a mass flow controller and iso or normal butane througha liquid metering pump followed by a back-pressure valve into thethermostatted preheater/mixing chamber. This chamber was a 11 stainlesssteel vessel which had been packed with borosilicate glass rings andelectrically heated. Mixed gases were then passed to the catalyst bed athigh temperature. The effluent from the reactor which was housed in aclam-shell electrical heater, was passed through a back-pressureregulator, through a liquid trap, a wet test meter, and through a gassampling bomb to vent. Periodic samples were analyzed by gaschromatography and mass spectrometry. Post-mortem analysis was conductedon aged catalysts.

EXAMPLE 14

A 4% Ni/3.5%Cs/Al₂ O₃ /S catalyst was prepared as follows: Gamma aluminagranules (110 ml), 18/35 mesh) were dried at 130°/2 hours then calcinedin a programmable furnace at 4° C./minute to 677° C., held at 670° C.for 1.5 hours, then heated at 4°/minute to 1080° and held for 2 hours.Nickel nitrate hexahydrate (11.67 g) was dissolved in dry acetone (26ml) of sufficient quantity to bring the solid alumina to incipientwetness (0.42 ml/g). After impregnation, the solvent was weathered off,the solid charged to a tube furnace and heated in flowing hydrogen to450° C. for 1 hour and cooled under nitrogen. Cesium nitrate (3.29 g)was dissolved in deioniized water to give 28 ml of solution. This wasused to impregnate the solid to incipient wetness. The solid was thendried in air at 130°, heated in flowing hydrogen to 450°, and held at450° for 1 hour. The sample was stored under N₂ until used.

EXAMPLE 15

A 3.3% Ni/2% Cr/SiO₂ catalyst was prepared as follows: Silica gelPQ-1231G of 18/35 mesh (186 g) was dried at 120° c. overnight. This wasimpregnated to incipient wetness with an aqueous solution (208 ml)containing Cr₂ O₃ (7.86 g) and dried at 120° C. overnight. The driedsample was then calcined in an ebullating bed under flowing air at 540°C. for 45 minutes, then cooled to 125° C. and held for 50 hours. Aftercooling, the solid was again impregnated to incipient wetness with anaqueous solution (208 ml) containing Ni(NO₃)₂.6H₂ O (33.4 g) followed bydrying at 120° C. A portion of the solid was then calcined in air at540° C./2 hours, flushed with nitrogen, then reduced in flowing hydrogenat 450° C./2 hours, cooled under H₂, and then stored under N₂ until use.ICP chemical analysis indicated 3.3% Ni, 2.0% Cr (VF basis).

EXAMPLE 16

A 3.4% Ni/3.4% Cr/4X Ba-L catalyst was prepared as follows:

Commercial zeolite n extrudate (Union Carbide lot 11842-31) was groundand sieved to give 103 g of 18/35 solid. An aqueous solution (500 ml)containing 12.2 g of BaCl₂.2H₂ O was used to ion exchange the zeolite asa stirred slurry at 80° C./30 minutes. A second exchange was thenperformed with a more concentrated solution (500 ml) containing bariumchloride dihydrate (30.1 g) for 30 minutes followed by distilled waterwashing (3×, 500 ml) and drying at 115° C. overnight. The sample wasthen placed in a programmable muffle furnace and heated at 9° C./minuteto 594° C. and held isothermally for 2 hours followed by cooling. Thesample was then re-exchanged with two batches of aqueous solution (500ml) containing 30.4 g barium chloride dihydrate per batch followed bywashing and calcining as per above description. The sequence of ionexchange followed by calcination was repeated two additional times.Chemical analysis by ICP indicated 8.4% Ba, 2.7% K, and 0.033% Na.Powder x-ray diffraction indicated highly crystalline materials of thecharacteristic spectrum for zeolite L.

Ba²⁺ L (40 ml) prepared as above was dried at 130° C. for one hour (3.4.g dry weight). Chromium trioxide (2.82 g) aqueous solution (18 ml) wasused to impregnate the zeolite to incipient wetness. After drying at130° C., the solid was heated in flowing air in a tube furnace held at540° C. for 1 hour and cooled. The solid was then impregnated toincipient wetness with an acetone solution (18 ml) of Ni(NO₃)₂.5H₂ (7.5g). After the solvent had been evaporated in an air draft, the samplewas reduced in flowing hydrogen at 450° C./2 hours, and stored undernitrogen until used. Chemical analysis by ICP indicated 3.4% Cr and 3.4%Ni.

EXAMPLE 17

A catalyst was prepared as follows:

This sample was prepared by following a variant of the procedure used toprepare the catalyst of example 16. After exchange of the zeolite asdescribed therein, the zeolite was first impregnated with chromiumfollowed by nickel impregnation using a similar procedure as aboveexcept heat. The sample was dried in a vacuum oven only after eachimpregnation. After drying of the fully impregnated zeolite at 120° C.,the solid was charged to a tube furnace and heated in flowing air at400° C./2 hours, cooled to room temperature under N₂, then N immediatelysulfided in a flow of 5% H₂ S/H₂ with gradual heating to 400° C. wherethe solid was held for 30 minutes. The sample was then cooled and storedunder nitrogen until use.

EXAMPLE 18

A 3.5% Ni/3.5% Cr/ZnAl₂ O₄ catalyst was prepared as follows:

A sample of zinc aluminate was ground and sieved to 18/35 meshand-calcined at 1500° F. for 1 hour. Chromium trioxide aqueous solution(4.02 g dissolved into 20 ml) was used to impregnate the zinc aluminateto incipient wetness. After oven drying at 300° C. overnight, the solidwas impregnated with 20 ml of an acetone solution of 9.96% nickelnitrate hexahydrate to incipient wetness. After evaporating the solid inan air draft and drying further at 230° C. under vacuum, the solid wastreated in a flow of 4% H₂ in N₂ while slowly raising the temperature to400° C. At 400° C., gas flow was switched to 100% H₂ and heatingcontinued for 1 hour followed by treatment with 5% H₂ S/H₂ for 0.5 hourat 400° C. After cooling, the sample was stored under N₂ until use. ICPanalysis indicated 3.5% Ni, 3.5% Cr.

Sulfiding was conducted by injection of measured quantities ofdimethylsulfoxide (DMSO) into the preheater section of the reactor aftercatalyst loading under flowing hydrogen. Temperature was ramped from400° C. to 550° C. over a three hour period, followed by additionalhydrogen flow for 3 to 10 hours at 550° to 600° C. prior to commencementof each run.

Hydrogen sulfide at levels between 2 to 200 ppm was sometimescontinuously fed along with hydrogen throughout each run. The higherlevels of H₂ S resulted in poor performance. Typical S/Ni ratios usedfor sulfiding with DMSO were 2-10.

All catalysts used were 18-35 mesh and some had been pre-reduced andbriefly sulfided with H₂ followed by passivation with 2% O₂ in N₂, toenable handling in room air while loading each reactor.

Occasional regeneration was performed by purging the system withnitrogen followed by introduction of air at 400°-510° C. for periods of3-8 hours. After another nitrogen purge, hydrogen was introduced tore-reduce the catalyst followed by resulfiding with DMSO and furtherhydrogen treatment. Time required for regeneration or sulfiding was notcounted as on stream time.

Test results from life testing are shown in Table IV for Ni or Ni+Crcatalysts on several supports. Each of the catalysts was sulfidedin-situ with DMSO. Various ratios of H₂ to butane were used; nobutadiene was detected during these runs. In some runs, partialregeneration was conducted after the catalyst had deactivated. Noattempt was made to completely regenerate; had regenerations beenconducted longer, all catalysts would probably have returned to theirinitial activities.

                  TABLE IV                                                        ______________________________________                                        Comparison of catalyst performance for iso-butane                             dehydrogenation in packed bed reactor                                         ______________________________________                                        Example 14:                                                                   GHSV = 900 h.sup.-1, H.sub.2 /iC.sub.4 H.sub.10 = 1.1-1.4, T                  = 600° C.                                                              4% Ni/3.5% Cs/γ Al.sub.2 O.sub.3 /S                                     Time On-Stream                                                                            Mole %      Carbon Selectivity To:                                (Hours)     Conversion  C.sub.4 ═                                                                         C.sub.4 ═ + C.sub.3 ═                 ______________________________________                                         2          18.3        89.6    92.1                                          19          14.8        92.1    94.4                                          22          15.1        91.0    93.2                                          45          14.9        94.9    97.3                                          48          15.4        91.8    94.1                                          80          11.5        91.3    94.2                                          98          13.4        87.7    90.4                                          ______________________________________                                        Example 15:                                                                   GHSV = 570h.sup.-1, H.sub.2 /nC.sub.4 H.sub.10 = 5.5, T = 597 ±            2° C.                                                                  3.3% Ni/2% Cr/SiO.sub.2 /S                                                    Time        Conversion                                                                              Sel. C.sub.4 ═                                      ______________________________________                                        54          41.2      27.3                                                    57          18.4      76.1                                                    60.5        17.9      74.2                                                    80          15.6      74.0                                                    104         13.5      74.0                                                    153         12.2      75.5                                                    183         11.0      74.0                                                    238          9.7      74.8                                                    262          9.1      74.8                                                    ______________________________________                                        Example 16: (Par. 1)                                                          GHSV = 650h.sup.-1, T = 602 ± 2° C., 3.4% Ni/3.4%                   Cr/4X XC Ba--L/S, H.sub.2 /iC.sub.4 H.sub.10 = 6                              Time        Conversion                                                                              Selectivity C.sub.4 ═                               ______________________________________                                        2           36.6      75.1                                                    4           34.3      81.0                                                    6           33.5      81.6                                                    27          30.0      83.4                                                    50          27.9      81.1                                                    65          22.2      78.8                                                    128         22.2      84.4                                                    155         20.8      86.0                                                    200         20.0      84.0                                                    223         18.4      84.8                                                    Partial Air Regeneration & DMSO H.sub.2 /iC.sub.4 = 3                         230.5       35.6      78.5                                                    251         29.8      81.3                                                    255         26.1      85.4                                                    275         23.8      85.4                                                    297         21.4      85.7                                                    330         15.6      86.3                                                    H.sub.2 Treatment                                                             358         20.4      84.7                                                    ______________________________________                                        Example No. 16: (Par. 2)                                                      GHSV = 650 h.sup.-1, T = 602 ± 2° C., 4% Ni/4% Cr/4X                XC Ba--L/S, H.sub.2 /iC.sub.4 = 3.5 ± 0.5                                  Time        Conversion                                                                              Selectivity To C.sub.4 ═                            ______________________________________                                        6           36.2      81.3                                                    26          30.4      82.3                                                    50          30.0      84.3                                                    77          23.6      84.2                                                    84          24.2      84.8                                                    108         22.6      84.7                                                    132         20.2      84.7                                                    155         20.0      84.5                                                    164         18.3      84.5                                                    184         15.7      85.4                                                    209         14.9      86.0                                                    214         15.0      87.2                                                    241         13.4      87.0                                                    258         13.0      87.0                                                    Partial Air Regen. & DMSO Sulfiding 10 ppm H.sub.2 S Co-Feed                  265         26.7      85.6                                                    275         24.6      87.0                                                    284         24.2      84.4                                                    304         22.4      84.6                                                    327         20.0      84.8                                                    358         17.3      85.8                                                    410         15.7      86.1                                                    430         13.9      86.7                                                    ______________________________________                                        Example No. 17:                                                               GHSV = 912 h.sup.-1, H.sub.2 /iC.sub.4 = 1.9, T = 602 ± 1° C.       4% Ni/4% Cr/4X XC Ba-L/S                                                                              Carbon                                                Time                    Molar Selectivities                                   On-Stream   Conversion  C.sub.4 ═                                                                         C.sub.4 ═ + C.sub.3 ═                 ______________________________________                                         1          22.1        87.5    91.5                                           2          20.0        87.5    91.7                                           8          16.2        88.7    93.1                                          11          15.1        88.7    93.1                                          27          12.8        88.9    93.5                                          31          12.6        87.1    91.6                                          51          10.9        87.0    91.5                                          52          10.5        91.6    96.3                                          Example 18:                                                                   GHSV = 950 h.sup.-1, H.sub.2 /iC.sub.4 = 1.9, T = 599° C., 3.5%        Ni/3.5% Cr/ZnAl.sub.2 O.sub.4 /H.sub.2 S                                       2          39.4        76.1    84.5                                           6          27.9        80.2    89.8                                          28          26.1        65.9    74.8                                          32          15.1        67.7    75.4                                          37          11.5        80.2    88.8                                          ______________________________________                                    

The data in Table IV show that these catalysts have good selectivitycharacteristics and are long lived. They may be regenerated. Comparisonof these data to data on similar catalysts sulfided with H₂ S makes itevident that the catalysts described here which had been sulfided withDMSO demonstrated higher selectivities and longer on stream lives thanthose sulfided with only H₂ S. Deactivation of the present catalysts ischaracterized by loss of activity rather than by loss of selectivity(probably due to loss of S) which was seen when only H₂ S had been usedas the sulfiding agent previously.

EXAMPLE 19

This example illustrates a method to modify the pore structure of thecatalyst support. 110 grams of gamma alumina (ALCOA CS-105) were treatedfor 2 hrs at 80°-90° C. in a 1.8M aqueous solution of oxalic acid, thenwashed with hot distilled water and filtered. The solid was thencalcined for 2 hrs in air at 910° C. The porosity in the range 10 to 50angstroms was drastically reduced while that in the range 50 to 200angstroms was significantly increased. In this particular case, the porevolume in the range 10 to 50 angstroms dropped from 0.16 ml/g in thecommercial alumina to 0.06 ml/g in the treated sample. On the otherhand, the pore volume in the range 50 to 200 angstrom increased from0.30 to 0.40 ml/g.

A preferred method to reduce acidity of alumina catalyst supports is theincorporation of cesium as described in Example 20:

EXAMPLE 20

110 ml of gamma alumina (United Catalysts CS331-4, 225 m₂ /g) 18/35 meshwere calcined in air for 1.5 hours at 1080 C. Then, the cesium was addedby incipient wetness of 3.29 g of cesium nitrate dissolved in 28 ml ofdeionized water and subsequently dried in an oven at 130 C.

EXAMPLE 21

20 grams of gamma alumina (United Catalysts CS331-9) 18/35 mesh,precalcined at 980° C. for 10 hours, were impregnated with an aqueoussolution of cesium nitrate (2.18 g. in 13 ml). After drying at 130° C.for 21/2 hours, the sample was further impregnated with a solution ofnickel nitrate in acetone (6.25 g of Ni(NO₃)₂. 6H₂ O in 20 ml). Thesample was dried in air at 180° C. and subsequently treated with NH₄ OH.This base treatment was done by spraying the liquid over the catalystusing a liquid/solid ratio of about 0.6 ml/g. The sample was reduced insteps (100° C./30 min. under H₂, kept at 600° C. for 2 hours, sulfidewith DM80 (0.07 ml/gr. wt.), cooled in H₂ overnight, passivated in 4% O₂/N₂ and stored.

Table V shows the improvement of nickel-cesium-alumina catalysts inselectivity towards isobutane dehydrogenation achieved as a result of adecrease in isomerization activity. The data in Table V show that thisdecrease can be either effected by addition of an extra amount of cesiumor by a calcination treatment before the loading of cesium. The catalystcontaining 3% Cs without a pre-calcination treatment exhibited arelatively high isomerization activity and poor selectivity. Bycontrast, the other two catalysts in Table V, the one with 7% cesium andthe pre-calcined one with a 3% cesium, exhibited high selectivities andno isomerization activity.

                  TABLE V                                                         ______________________________________                                        EFFECT OF ACIDITY ON SELECTIVITY                                                      SELECTIVITY %                                                         CATALYST  dehydrogenation                                                                           isomerization                                                                             hydrogenolysis                              ______________________________________                                        8% Ni 3% Cs                                                                             75          20          5                                           on Al.sub.2 O.sub.3                                                           8% Ni 7% Cs                                                                             87          0           13                                          on Al.sub.2 O.sub.3                                                           3% Ni 3% Cs                                                                             89          0           10                                          on pre-calcined                                                               Al.sub.2 O.sub.3                                                              ______________________________________                                    

FIG. 8 of the drawings shows the reduction in TPD peak areas of pyridinedesorption rate for the three catalysts whose selectivity data are shownin Table V. The sizes of the peaks observed between 130 and 500 C are ameasure of the degree of support acidity. It can be clearly seen thateither the addition of extra amounts of cesium or the pre-calcinationbefore the loading of cesium diminishes the support acidity.

The following examples illustrate the catalytic performance of thepreferred catalysts of this invention as compared to other, knowndehydrogenation catalysts:

EXAMPLE 22

25 g. of zinc aluminate, 20/40 mesh, were impregnated with 0.26 g ofchloroplatinic acid and 0.11 g. of stannous chloride dihydrate dissolvedin 9 ml of distilled water. The sample was dried overnight in an oven at110° C. Then it was calcined at 300° C. for 1 hour, re-sieved, andstored.

EXAMPLE 23

32 g. of gamma alumina (Alcoa S-100), pre-calcined at 950° C. for 2hours, were impregnated with 57 ml of a 2.1M KOH solution. After dryingat 140° C., the sample was sequentially impregnated with Pt(NH₃)₄ Cl₂and SnCl₂ aqueous solutions, and calcined to yield a sample containing0.39 weight percent Pt. and 0.39 weight percent Sn.

The iso-butane dehydrogenation rates over the catalyst of Examples 21,22 and 23, are given in FIG. 9 as a function of time on stream. Theserates were obtained in a packed bed reactor, operating at 600° C., 15PSIA, with LHSV of 1 to 1.5 and an H₂ to iso-butane ratio between 1.0and 2.0. It is demonstrated that the preferred catalyst of Example 21 issuperior to the Pt-based catalysts of Examples 22 and 23 in terms ofactivity and stability.

EXAMPLE 24

This example illustrates the use of a temporary pore filling reagent toachieve preferential deposition of the nickel catalyst component in thelarger pore region.

39.60 grams of gamma alumina (Alcoa CSS-105) ground and sieved to 18/35mesh were calcined in air at 950 C for 2 hrs. The alumina was thenimpregnated with 8.00 cc of ethylene glycol at room temperature andplaced in an oven at 197 C for 5 min. The amount of ethylene glycolremaining in the catalysts was found to be 5.35 g, which corresponds toabout 0.125 ml/g catalyst. Due to capillary effects, the condensation ofethylene glycol at its normal boiling point should occur in the smallerpores. The subsequent incorporation of nickel was done by incipientwetness impregnation of 11.92 grams of nickel nitrate (Ni(NO₃)₂.6H₂ O)dissolved in 24 ml of acetone. The impregnated sample was then dried inair at 140° C. for 25 min and then calcined at 500° C. for 2 hrs.Finally, to reduce the acidity of the support, cesium was incorporatedby incipient wetness of 1.84 grams of cesium nitrate dissolved in 24 mlof distilled water. Then, it was dried in air at 100° C. for 8 hrs andcalcined at 550° C. for 2 hrs.

EXAMPLE 25

This example illustrates the deliberate preformation of a barrier layerby repeated impregnation-calcination steps such that the firstcalcination is above 500° C. in oxygen or air, followed by one or moresubsequent impregnation--low temperature calcination steps. This layerhinders or prevents the formation of nickel aluminate during calcinationor catalyst regeneration at high temperatures.

38.25 grams of gamma-alumina (Alcoa CSS-105), 18/35 mesh, wereimpregnated with 2.50 g of Ni(NO₃)₂.6H₂ O dissolved in 28 ml of acetone.The sample was subsequently dried in an oven at 250° C. for 1 hr andthen calcined in air at 500° C. for 1 hr and at 950° C. for 2 hrs. Afterthis treatment, the color of the sample was a light bluish green. Thesecond addition of nickel was also performed by incipient wetnessimpregnation using 12.58 g of nickel nitrate dissolved in 29 ml ofacetone. This time, the sample was dried at 100° C. for 1 hr and mildlycalcined at 200° C. for 2 hrs. The final step was the addition ofcesium, following the procedure explained above for other samples.

EXAMPLE 26

2.0 grams of alumina (United Catalysts CS 331-4), pre-calcined at 1000°C. for 10 hours were impregnated with an aqueous solution of 0.36M(Cu(II) acetate using a liquid/solid ratio of 0.6 cm³ /g., resulting ina copper loading of 1.38 weight percent. After drying in air, the samplewas calcined at 600° C. for 1 hour. Subsequently, it was impregnatedwith Ni nitrate in acetone using a liquid/solid ratio of 1.0 Cm³ /g. toyield a nickel loading of 3.7 weight percent.

The sample was then dried at 130° C. and reduced in H₂ at 600° C. Thetemperature programmed reduction profiles in FIG. 10 illustrate theeffect of the barrier layer on the reducibility of nickel on thecatalysts of examples 21 and 27.

Increasing the calcination temperature makes it more difficult to reducethe nickel, but when a Cu barrier layer is present, this effect isgreatly reduced. In this case, a large fraction of Ni can still bereduced even after calcination at 600° C.

EXAMPLE 27

A catalyst prepared according to Example 28 was tested for selectivehydrogen-combustion as described in Example 26 but with a different feedcomposition and gas hourly space velocity. Feed composition was 18.25mol % CH₄, 4.14 mol % H₂, 62.78 mol % isobutylene, 4.28% O₂. Reactorpressure was 110±10 psig during the runs. The results are tabulatedbelow:

    ______________________________________                                                                             Oxygen                                                                        Atom                                     T    GHSV      H.sub.2   O.sub.2     Selectivity                              (°C.)                                                                       (h.sup.-1)                                                                              Conversion                                                                              Conv.   R   To Water                                 ______________________________________                                        549  18323     85.4      96.2    5.3 76.8                                     537  "         88.5      91.0    4.3 72.7                                     571  "         79.1      94.6    4.0 70.6                                     569  "         81.4      87.3    3.1 64.7                                     458  "         54.8      32.5    6.3 78                                       453  "         75.3      27.8    5.5 75                                       485   9162     87.8      99.7    5.3 76.5                                     497  "         92        99.8    4.4 72.7                                     538  "         92        99.7    4.5 73.4                                     ______________________________________                                    

Oxygen atom selectivity to water is defined as: ##EQU1## in the productstream.

EXAMPLE 28

This example illustrates preparation and testing of catalysts for theselective combustion of hydrogen.

Catalysts for selective hydrogen combustion were prepared then tested ina steady state continuous reactor system.

Stannic chloride pentahydrate (38 g.) was dissolved into 75 ml ofdistilled water. Phosphoric acid (85%, 9.5 g.) was dissolved into 40 mlof distilled water. These solutions were combined as solution A.Ammonium hydroxide (concentrated, 35 ml) was diluted with 200 mldistilled water. The resulting solution was labeled B. The twosolutions, A and B, were alternatively added to a beaker containing 50ml of distilled water stirred with a magnetic stirrer and fitted with pHelectrodes. pH was maintained in the range 3-4 until the entire amountsof A and B had been added. The resulting white precipitate was collectedfiltration, washed with distilled water 3 times, and dried at 125° C.overnight in air. The solid was then ground and sieved to 18/35 mesh.

A feedstock composed as follows was used to simulate product fromdehydrogenation processes as disclosed herein and was passed over thecatalyst at steady state conditions at various temperatures in a packedbed reactor. On-line analysis of products enabled relative catalystperformance to be gauged:

    ______________________________________                                        Mol. % Feed Composition                                                       ______________________________________                                                H.sub.2                                                                             11.07                                                                   O.sub.2                                                                             5.05                                                                    N.sub.2                                                                             19.65                                                                   H.sub.2 O                                                                           0.269                                                                   CH.sub.4                                                                            30.66                                                                   iC.sup.4 H.sub.10                                                                   0.054                                                                   iC.sub.4 H.sub.8                                                                    33.23                                                           ______________________________________                                    

Total GHSV was about 30,000 h-1 in these tests. On stream times ofseveral hours at each temperature were achieved. A selectivity term, R,was defined: ##EQU2## where H₂ O, CO, CO₂ refer to those components inthe product gas stream.

Given the feed composition, completely random combustion of anycombustible feed components that impinged on the surface would result inan R value of 1.3. R values above about 2 indicate some degree ofpreferential combustion of hydrogen rather than of either methane orisobutylene. Acceptable in this screening test catalysts have R valuesabove about 4 at ≧95% O₂ conversion.

Catalysts were tested at various temperatures between 300°-600° C., butonly high temperature data are reported here since these reflect themost useful temperature range of the process.

Table VI lists comparative data for various compositions including thoseof the present invention. R values were determined by product analysisin which the molar composition of each component was measured by amultidimensional GC technique.

Table VI shows the results obtained with catalyst according to thisembodiment of the invention, number 6, catalyst prepared according toExample 1 of U.S. Pat. No. 4,788,371, number 5, and other catalystsshowing substantially lesser degrees of activity for the selectiveoxidation process, numbers 1 through 4. Comparison of catalysts 5 and 6shows higher selectivities for the catalyst according to the invention,number 6, at the high temperatures, 560° C. and above.

                  TABLE VI                                                        ______________________________________                                        COMPARISON OF CATALYSTS FOR HYDROGEN                                          COMBUSTION AT STEADY STATE                                                    (2-4 HOURS ON STREAM: GHSV ˜ 30,000 h.sup.-1)                           CATALYST              T (°C.)                                                                        R                                               ______________________________________                                        1.      Cu.sup.2+ Exchanged Zeolite 3A                                                                  549     2.1                                                 Diluted 1:1 with αAl.sub.2 O.sub.3                                                        549     1.9                                         2.      Cr.sup.3+ Exchanged Zeolite 3A                                                                  442     1.4                                                 Diluted 1:1 with α Al.sub.2 O.sub.3                                                       478     1.8                                                                   552     1.6                                         3       α-Al.sub.2 O.sub.3                                                                        565     2.0                                                                   561     2.0                                         4       4% Ni/3.5% Cs/Al.sub.2 O.sub.3                                                                  459     1.6                                         5.      *Pt/Sn/Cs/Al.sub.2 O.sub.3 Diluted                                                              563     3.5                                                 1.1 with αAl.sub.2 O.sub.3                                                                572     4.1                                                                   508     10.4                                                                  504     6.1                                         6.      SnPO.sub.4 Gel    560     4.3                                                                   574     5.1                                                                   466     4.9                                                                   449     5.0                                         ______________________________________                                         *Catalyst prepared according to Example 1 of U.S. 4,788,371                   .sup.+ The invention                                                     

The invention claimed is:
 1. In a process of selectively oxidizinghydrogen in a mixture with other gaseous material by contact with acatalyst under hydrogen oxidation conditions, the improvement whichcomprises using as catalyst in said oxidizing a phosphate of a metalselected from the group consisting of germanium, tin, lead, arsenic,antimony, and bismuth.
 2. Process according to claim 1 wherein saidcatlayst is a phosphate of tin.
 3. Process according to claim 1 whereinsaid conditions include temperature in the range from 430° to 600° C. 4.In a process for selectively oxidizing hydrogen in a mixture with othergaseous material by contact with a catalyst under hydrogen oxidationconditions, the improvement which comprises using as catalyst in saidoxidizing a composition consisting essentially of a phosphate of a metalselected from the group consisting of germanium, tin, lead, arsenic,antimony, and bismuth.
 5. Process according to claim 4 wherein saidmetal is tin.
 6. Process according to claim 4 wherein said conditionsinclude temperature in the range from 430° to 600° C.